Comment 3 for bug 66188

Still there (or it's a new one with the same effect) in 2.17.90 at least with Ubuntu patches.

It's not only with the Escape key or the Cancel button, but with all of them:

from /proc/id/smaps (no swap)

before switching user

31769000-3422f000 rw-p 31769000 00:00 0
Size: 43800 kB
Rss: 43800 kB
Shared_Clean: 0 kB
Shared_Dirty: 0 kB
Private_Clean: 8760 kB
Private_Dirty: 35040 kB

After

31769000-34509000 rw-p 31769000 00:00 0
Size: 46720 kB
Rss: 46720 kB
Shared_Clean: 0 kB
Shared_Dirty: 0 kB
Private_Clean: 8760 kB
Private_Dirty: 37960 kB

Note:
1) the patch is after debian/rules apply-patches
2) there's more leaks but they are small.