TTH differs once file is actually shared

Ok, here's the problem;

I was once told, by several people, that they couldn't download 2 files from me, because their client said they were empty.
When I checked the files in question, both via the SFV-file, and by actually unpacking the files, they worked just fine.
I used tthsum so look at the TTH for the file, and noticed that the one in my filelist was different, and that the 2 files actually had the same TTH in my filelist.
Since I knew the files were fine, I tried refreshing, and rebuilding when that didn't work. No joy.
Next, I tried removing the file, rebuilding, and dowloading it again (as someone else had it at the time), checked the with the SFV-file, and refreshed since the file was fine. As I recall, I repeated this a couple of times, and even restarted the client a few times, before it finally worked.

Everything was fine for some time, until I got a message from someone saying there was something wrong with one of the files. One of the original 2, in fact :) Checked, and lo and behold, the TTH in dc++ is different from the one I get from tthsum, and the file is still OK according to the SFV-file, and, yes, I can unpack..

IIRC, I used 0.7091 last time, and now I'm using 0.75