[Svnmerge] How does/should svnmerge deal with its own commits?

[Hendrik Kueck]

I am confused about how svnmerge deals with its own commits on other branches. 
Let me clarify: 
Let's say I have one branch and trunk and do bidirectional merging. I do a 'svnmerge block' on the trunk to tell it that I want to ignore some revision of the branch. I commit this change on the trunk. If I now go to the branch and do a 'svnmerge avail -b" it will list this commit as available for merging. It seems to me that ideally svnmerge should not even display this commit. What happens if I accidentally or intentionally merge such a svnmerge commit? Could this be harmful in some circumstances?