The buttons for the bank are getting priority over the chatbox and is overlapping it:
http://prntscr.com/93hs11

EDIT:

I also found that if you hover the back window close to the edge of the screen, making the bank window overlap with the border of the screen, the borders and background disappears:
http://prntscr.com/93hvz2

EDIT 2:

This also goes for items; also overlapping the chatbox