If you press "k" with nothing targeted to open the PDA for yourself, then press the key to see the Accomplishments screen, then press "k" again, the PDA closes. If you press "m" to open the PDA mission screen, then "v" to see the "Advancement Log", then "m" again, the PDA goes back to the Mission Log tab. This is inconsistent and somewhat quirky behavior that's been annoying me for awhile. Personally, I think that once you switch to another tab in the PDA (ie: Accomplishments or Advancement Log), pressing the original button ("m" or "k") should bring you back to the tab that you first opened instead of closing the PDA, but that's really a design choice. Just pick one method and stick with it.

Agreed. Inconsistent interfaces bug the living crap out of me.

Ok, pressing k shouldn't close the window if you don't have that tab open. I must've missed that.