Hello,
I don't know whether this is a known bug:
There is a problem with headlines not well-formed. I grabbed some examples from the German Wikipedia:
== wrong headline
== Italienisch ==stimmt das denn??
Both lines are not parsed as headlines, but when you edit a section of the article containing these lines you get a different section from what you expected, because it seems that the software increments the section counter at these lines, too.
Eckhart