I did some further debugging and testing and found that the reason I experience different behavior between 2.0.1 and 2.0.2 is different than initially thought.
I have disabled auto xposting based on the category which is set by my RSS reader and in 2.0.1. these posts are indeed not xposted. When I enabled this category for xposting in 2.0.1 I found that xposting did NOT occur at all. It looks like this is because of missing user rights and that this "issue" has been resolved in 2.0.2. So, the reason my RSS imported posts were not xposted in 2.0.1 is because of an issue later resolved in 2.0.2.
I also inserted some logging in the 2.0.2 version (right at the start of the function "transitionPostStatus") to inspect the post category. I found that every post from my RSS category hits this function four (!!) times and the first time the category is set to "Local post". It looks like this triggers the xposting as the category "Local post" is setup for auto xposting. The 2nd, 3rd and 4th time the same post has the category I disabled from auto xposting but at that time the forum topic is already created from the 1st time this function is called.
I also checked with creating posts manually and found out that if I created a post manually in a category that is enabled for xposting the xposting did occur (as expected). Changing the post category later on to a category that is disabled does not remove the forum topic. The other way around (start with the disabled category and change later to an enabled category) does create the forum topic at the time I change the category to an enabled category.
QUESTION: is it expected behavior that the forum topic is NOT removed when changing the category of the WP post to a category which is disabled for xposting.
In case this is expected behavior I need to created a workaound so that my RSS importer does not save the post with the category "Local post" before changing it to the category I disabled from xposting.
Many thanks for looking into this.