Godot version:
3.1 9e62826
OS/device including version:
Windows 10
Issue description:
When my BBcode in RichTextLabel is like below, everything works as I expect:

[center][color=green]Ziemniakq[/color][/center]
but when I change text to this, then strange text after my text appear

[center][color=green]Ziemniakq[/center][/color]
Minimal reproduction project:
Test.zip
But why do you close tags out of order?
BBcode on forums doesn't care about order, and it's an easy enough mistake to make.
Well, forums run on servers with many gigabytes of RAM and many GHz CPUs, and general developers are much more disciplined. I doubt making fuzzy parser for bbcode worth the gain at all. Just my personal opinion.
State of this issue: since 3.2, the MRP with reversed close tags produces "Ziemnikq[/center]", which is a fair improvement on 3.1.
Yes that seems correct to me, unless we aim to explicitly support closing tags in random order, but I don't think it's necessary.
Most helpful comment
BBcode on forums doesn't care about order, and it's an easy enough mistake to make.