Me again! Now trying to get some fanfic back into personal documents... and the Kindle won't let me!

[anolinde.livejournal.com]

So, I just posted about putting fanfic under the "Books" section of the Kindle Fire. However, given that *ahem* some of the fanfics I've downloaded are a bit, erm... shall we say... I don't really want them in the Books section where most people are going to look... I realized that it's probably better if I leave them in the "Personal Documents" section.

Only, now the Kindle won't put them back! I've run them through Calibre again and added the [PDOC] tag, but they're still showing up as "Books." Anyone know why this might be happening? I've already tried two customer service reps at Amazon and they have no idea. :(

Sorry for so many posts in so few days! Bit of a noobie here, lol.

EDIT: To clarify, they're all .mobi files.