Another tricky problem I was running into.
Tricky because I can't reproduce it
When pressing the key bound to "wq_buy" (Buy menu), the menu appeared but disappeared immediately. So I could not buy anything.
The only way I find to stop this behaviour is to exit back to WQ3 main menu and restart a game.
If anyone has ever seen it, please report too, as I don't really know in what WQ3 version the problem occurred.