To make things short
You MUST write the bio in the FIRST map you enter, and then MUST relogg in order for it to save.
If you make a bio in the 2nd, 3rd map you enter, the bio will not be changed.
If the game crashes or ends inappropriately, the bio wont be saved
If you edit an already saved bio from another map than the first one it might disappear as well.
It's a game bug that's been there from the start. Sorry for this.
Hopefully we will get client sided bios sometime in the future that would prevent this.