Hitting "Esc" during mouse button control assigment breaks the control assignment screen

1. Continue a save or start a new game.
2. When the game has loaded (or the intro phase is over), hit Esc to bring up the ingame menu.
3. Go to Options > Controls.
4. Click on any assigment field in the Mouse column.
5. When the assignment popup appeared (with the countdown at the bottom), hit Esc.
6. The entire ingame menu is closed and you get returned to the game.
7. Hit Esc and go to Options > Controls again.
8. The screen is now unresponsive other than being able to scroll the assignment list with the mousewheel, and the "DONE" button is also transparent/greyed out.

NOTE: This only happens while in a game, but not from the main menu.

I've observed this in 0.62b1, but might be also the same in the current live release.