If your account is about one day old, yes it's a great idea to have UI elements close due to damage. However, if you are more than a day old, the UI closing due to damage is not only annoying, it's insulting.

These dont work for you?

Settings -> General Settings -> Misc. -> Close UI When Hit
Slide it to Off

It just takes a few seconds looking through the menus to find. If your account is more than a day old, you may want to look through the settings menus to see all the great stuff in there before you feel insulted.

For some menu, such as inventory, this works to stop the UI from closing. For other UI menus, such as the map or skill menu, this will not work.

Oddly enough, the pearl shop UI menu cannot be closed due to damage. I wonder why.

Unfortunately the toggle doesn't work for more than half of the menus. Hopefully they'll fix this issue later on because it's a pain when you're trying to equip your weapon while being attacked, only to have your UI disappear on you regardless of the toggle status.

This comes up in google search firsr. So sorry for the necro. It's in the same spot but they renamed it.

.... They fixed the issue the OP posted about 2 years ago.  It was bugged.  Don't necro posts from 3 years ago dude.