This issue arises mostly at startup but sometimes even when switching characters during play.
When I start the game (and the computer is still heavily accessing the hard drive) and select the character in the 8th slot, the name, class, location and the other information is displayed immediately while the main window remains black for some time (a couple of seconds). When I choose play during this time, the character from the 1st slot is loaded and logged in instead of the selected one in the 8th slot.
This happens too when switching characters in play but not as often and not as often with characters that were logged in recently (about one hour I think).
I’d guess that this character slot isn’t immediately preloaded as it isn’t displayed along with the first 7 slot but only accessible by scrolling to the right.