I left someone red rep an hour back and I'm pretty sure that it went through as I got the confirmation, but 1 point hasn't been deducted from my rep. I can give the details via PM if needed. Maybe it's a VB4 thing?
where did you give the rep? was it a low rep area? i think, i may be wrong, but some areas it doesn't cost as i have seen this too.
I have noticed this also, I believe rep was changed around a few weeks back. I think the new system doesn't -1 your rep unless u have high enough rep for it can count against theirs.