Hi.
I have a work around. Just tested this on PS4. In the Vab, select the Item you want to purchase. Switch to cursor mode, and bring the cursor to the place, where the purchase button is. I know, that the window will disappear. Switch back to normal mode (l3) keep the item highlighted, and open the options. Close the option menu, and switch to courser mode. The window will now stay open, and its possible to hit the purchase button.
Greetings
Matze