Events Passing Hardcoded Same-Flavor ml+l- Cuts

Dear Experts,

I am studying WZ + 2j -> 3 lep + 2j + MET and want to investigate the ttbar + W background. I am trying to hardcode into setcuts.f and cuts.f a cut that will reject any event that does not contain
(a) a pair of oppositely charged leptons that (b) have the same flavor and (c) are in a window around mZ.
The problem is that I am finding events in my .lhe file that do not pass this criteria.

I attempt hard code my cuts into MG5 in a two-step fashion. In setcuts.f, I create boolean objects, similar to is_a_a(i) or is_a_j(i) and pass this to cuts.f. In the latter file, I ask for any same-flavor, opposite sign leptons.

In setcuts.f I have added
(Added near the beginning of the file)
      LOGICAL IS_A_EP(NEXTERNAL),IS_A_EM(NEXTERNAL)
      LOGICAL IS_A_MP(NEXTERNAL),IS_A_MM(NEXTERNAL)
      COMMON /TO_SPECISA/ (... default stuff....), IS_A_EP,IS_A_EM,IS_A_MP,IS_A_MM

(Added at the beginning of the first i=nincoming+1,nexternal loop)
         is_a_ep(i)=.false.
         is_a_em(i)=.false.
         is_a_mp(i)=.false.
         is_a_mm(i)=.false.

(Added a little further down in the same loop)
         if (idup(i,1,1).eq.(-11) ) is_a_ep(i)=.true. ! e+
         if (idup(i,1,1).eq.(-13) ) is_a_mp(i)=.true. ! mu+
         if (idup(i,1,1).eq.( 11) ) is_a_em(i)=.true. ! e-
         if (idup(i,1,1).eq.( 13) ) is_a_mm(i)=.true. ! mu-

At this point, I believe I have assigned my boolean objects the appropriate T/F values.
In cuts.f, I have added
(Added near the beginning of the file)
      LOGICAL IS_A_EP(NEXTERNAL),IS_A_EM(NEXTERNAL)
      LOGICAL IS_A_MP(NEXTERNAL),IS_A_MM(NEXTERNAL)
      COMMON /TO_SPECISA/ (... stuff that remains unchanged from default file... ) IS_A_EP,IS_A_EM,IS_A_MP,IS_A_MM
      integer zCounter
      double precision mZRng

(Added right before s-channel min & max invariant mass cuts are made)
      mZRng = 12.50D0
      zCounter = 0

      do i=nincoming+1,nexternal-1
         do j=i+1,nexternal

(Here I am asking if I have any same-flavor and oppositely charged leptons)
(Edit: The ampersands here are fortran line continuation flags)
            if( (is_a_ep(i).and.is_a_em(j)) .or.
     & (is_a_em(i).and.is_a_ep(j)) .or.
     & (is_a_mp(i).and.is_a_mm(j)) .or.
     & (is_a_mm(i).and.is_a_mp(j)) ) then

(Here I am asking if the invariant mass is less than 91.2 + 12.5 GeV and greater than 91.2 - 12.5 GeV)
               if( (dsqrt(Sumdot(p(0,i),p(0,j),+1d0)).LT.(91.2D0+mZRng))
     & .AND.
     & (dsqrt(Sumdot(p(0,i),p(0,j),+1d0)).GT.(91.2D0-mZRng))
     & ) then

( If I have a Z candidate, then I increment my Z Counter)
                  zCounter = zCounter + 1
               endif ! in mZ Range
            endif ! (e+,e-) or (e-,e+) or (mu+,mu-) or (mu-,mu+)
         enddo
      enddo

(If I have no Z candidate, then I reject the event)
      if(zCounter.eq.0) passcuts=.false.

To clarify, in my runcard.dat file, the following line has been set:
   T = cut_decays ! Cut decay products
The minimum and maximum invariant mass for pairs have been set to 0 and -1, respectively.

Now here is the kicker. For the process
define w = w+ w-
define l = l+ l-
define v = vl vl~
generate p p > t t~ w QCD=2 QED=1, t > b l v, t~ > b~ l v, w > l v

my resulting .lhe file has events like the one below where there is one one e+ and two mu-. Already this is a bad sign since there are no same-flavor, oppositely charged pairs. The invariant masses are m(e+mu-1) = 292 GeV and m(e+mu-2)= 109 GeV, which is also outside my mZ window (91.2+/-12.5 GeV). My data is mostly populated with my desired data, but I cannot seem to rid myself of these events.

<event>
15 0 0.2041000E-07 0.6854600E+03 0.7546771E-02 0.1028105E+00
       -2 -1 0 0 0 501 0.00000000000E+00 0.00000000000E+00 0.24501702010E+03 0.24501702010E+03 0.00000000000E+00 0. 1.
        1 -1 0 0 502 0 0.00000000000E+00 0.00000000000E+00 -0.14051334493E+04 0.14051334493E+04 0.00000000000E+00 0. -1.
      -24 2 1 2 0 0 0.92025752585E+02 -0.11709766887E+03 -0.90199089798E+03 0.91769962143E+03 0.80027569917E+02 0. 0.
        6 2 1 2 502 0 -0.16519660079E+03 0.97615337913E+02 0.13859680161E+03 0.29270001876E+03 0.17217885020E+03 0. 0.
       24 2 4 4 0 0 -0.78710286332E+02 0.21054620753E+02 0.10659082841E+01 0.11303849640E+03 0.78345129253E+02 0. 0.
       -6 2 1 2 0 501 0.73170848209E+02 0.19482330959E+02 -0.39672233282E+03 0.43975082919E+03 0.17395013126E+03 0. 0.
      -24 2 6 6 0 0 0.45405874961E+02 0.23388338823E+02 -0.39998715766E+03 0.41113440529E+03 0.80206390323E+02 0. 0.
        5 1 4 4 502 0 -0.86486314462E+02 0.76560717159E+02 0.13753089333E+03 0.17966152237E+03 0.46999998093E+01 0. -1.
      -11 1 5 5 0 0 -0.64694693043E+02 0.84043659919E+01 0.35127366336E+02 0.74094321924E+02 0.00000000000E+00 0. 1.
       12 1 5 5 0 0 -0.14015593289E+02 0.12650254761E+02 -0.34061458052E+02 0.38944174473E+02 0.00000000000E+00 0. -1.
       -5 1 6 6 0 501 0.27764973248E+02 -0.39060078637E+01 0.32648248436E+01 0.28616423892E+02 0.46999998093E+01 0. 1.
       13 1 7 7 0 0 -0.18411721052E+02 0.18288404331E+02 -0.63274953876E+02 0.68389889553E+02 0.00000000000E+00 0. -1.
      -14 1 7 7 0 0 0.63817596012E+02 0.50999344918E+01 -0.33671220379E+03 0.34274451574E+03 0.00000000000E+00 0. 1.
       13 1 3 3 0 0 0.77625165146E+01 -0.73737860294E+02 -0.37617999987E+03 0.38341742397E+03 0.00000000000E+00 0. -1.
      -14 1 3 3 0 0 0.84263236070E+02 -0.43359808577E+02 -0.52581089811E+03 0.53428219746E+03 0.00000000000E+00 0. 1.
</event>

I appreciate any and all advice.

Best Wishes,
Richard