Many thanks for taking the time to leave us a post on here. Also, I can see that it’s your first post on the forum, so welcome to the community!
This is odd. I’ve just tested on my end and have not been able to replicate the bug. May I just ask, which device and system version on the device are you using Panda on?
Also, when you quit/restart Panda and attempt this again, does the same bug occur?
I had a similar issue today in macOS latest Panda. I changed the header size in a big document and then a bunch of text under it went white (painted over). It stayed that way until I highlighted the text.
I consulted a member of the development team regarding the above. It’s just a rendering artifact, it’s nothing problematic, but it’s something we definitely want to get rid of.