Translation not displaying correctly

Hi, I have installed a localized wordpress version. I updates a few times and the translation was not ready, so I did the english update. The bulgarian team doesnt seem to be active anymore, so I did only english updates. Then I saw that the bulgarian translation for 3.5.1 is 100% completed on translate.wordpress and I downloaded the .mo and .po files. Renamed them to bg_BG.po and .mo and uploaded them to my WP installation. So far so great. BUT now the translation is showing only partially, and I don’t know why. Some of the stuff are translated, some of them are not (and the file is 100% translated, no english strgins at all). I thought that maybe the people submitted the original english string as a translation, but no, the string is acutally translated but it’s not appearing on my installation. It’s a weird issue, so I hope someone can help me resolve it, because it’s pretty annoying.

Thannks in advance!