This is happening on WoW Classic Era at Hardcore and non-Hardcore realms.
I tested on different characters, no addons are turned on, the behaviour is the same.
Whenever you try moving a draggable element such as your avatar but by accident press the left and the right mouse button at the same time for a couple of seconds, the mouse cursor will get stuck to the element and won’t release unless you do a “/reload”. There are no addons turned on, so not an addon issue. The issue seems to be present on the classic client only.
This seems to be the same issue described at https://eu.forums.blizzard.com/en/wow/t/workaround-for-map-button-stuck-mouse/462250/2 on Aug 10.
This can be quite detrimental on a hardcore environment as you are not able to click on anything if your mouse is stuck to the element you are dragging.
Possible workarounds (not solutions):
- Do a “/reload”.
- If you can, lock the element when you are comfortable with its position so you don’t try moving it by mistake.