well, to describe it from the start:
i have a 1430 max VP
i wanted to buy the helmet in the wind's sanctuary which costs 1600 VP
so i went to the free credits page and opened/voted on all sites there (since that gives free VP also)...
now, since it doesn't refresh the current VP (and all other stats) right away, i usually go idle and come back right away for it to refresh... but this time i didn't since i was close to the next regeneration (and that would take away all VP i had over 1430)...
so i went to the shop right away, wanting to buy the helmet...
just as i was about to do it, i noticed that i could buy body armor too (since it didn't say "no credit" next to it's price), so i thought "why not buy the better thing"
so, i bought the body armor and it turned out i didn't have enough for it
i got the armor and my VP went down to -3 (which means i was 3 VP short to buy the armor)
donno if it's a bug (or the game taking pity on me for being so close), so i decided to post it and see.