White screen crash when opening multiple clients

[Schattengaenger]

Hi,

first off: I tested this with the default client and a personal one. Since they both show the same problem I am inclined to believe it is a default problem.
Let's say you want to have an alt online. What do you do? You minimize the first client, open a second window of the same client and log in with the second account. Going back to the first client now shows a blank, white window that cannot be closed short of using the task manager to kill it.

A friend suggested it is a driver issue, and having downloaded one it seemed to go away, but only for maybe a single playsession. The next day, the same problem and the GPU driver IS up to date.

Any suggestions on what I should do? (Except not play with multiple client windows)