Big problem with svn:mergeinfo, feature branches and merging (reintegrate)

Hi,

I have big problems with _reintegrating feature branches_. I have this problem only with *_one reposity location_*.

_I show it on example_:
1) I create branch ( _feature branch_ )
2) I switch to this branch
3) *_I change/edit only one file in this feature branch!_* and commit ( the filename which i change is *_assets\CrystalShop\Crystal\Shop\Abstract.php_* )
3) I switch back to trunk and try reintegrate this feature branch back to trunk
4) the result looks like this ( I show it with the help of the TortoiseSVN ):
I decided, that I create video where is everything showed, so here is the link to the captured screen, it's online on Vimeo server ( you can watch it in web browser ):
http://vimeo.com/12973409

I must solve this problem somehow and I want to know 3 things:
- not what cause this problem, because I know that *svn:mergeinfo* properties on the _subdirectories_ and on the _files in the subdirectories_ cause this, BUT WHY IT'S SO?
- how to prevent this problem?
- and how can I resolve this problem ( I don't want to delete *svn:mergeinfo*, but as I can see *_it's only one possible solution_* :(, or i'm wrong?? )

When someone decide to help me or know how to resolve this problem, but need some more info about the properties in my repository ( or anything else related to the SVN repository ), I can create user for this repository ( can provide read access ),
because I have my own public IP address.

Thanks for any advices and suggestions, because the issue priority it's very critical and blocker for our company.