Found this bug just now. It's an UI bug, not sure if easy to fix.
Log in with a character.
Open ESC menu.
Click to open a buyshop from other character. Do not close it.
Click character select.
Log back in (or even with other character, doesn't matter, not sure if needs to be in the same map).
Click buy shop.
CRASH.
Game will either just close or give you a Gravity Error Handler but will freeze.
Only option is to close RO entirely.
Tested in 2 PCs, multiple times. Same result every time.