I did not know of any parent windows and to me it looks like there is none. Can you point me to this unused code you mentioned?

Back to the topic, on the "deposit money" problem in the shopkeeper interface, the function "EndItempointer()" has the code to manage it (I don't remember in which file it is). The code is activated if the current screen ("guiCurrentScreen" variable) is "SHOPKEEPER_INTERFACE_SCREEN". Unfortunately, the "current screen" is the Yes/No message box which asks if you really want to deposit money. When the screens were managed with flags, a memory of the shopkeeper interface existed there and the code tested it rather than the current screen.