Mendix will generate an xsd in the data\tmp folder every time a xml mapping is triggered. I know Mendix doing this, but is there a specific reason to keep these files on disk? Of course I can delete those files every x days manually or with a script, but with 20 applications on 10 different environments, it could be automated by the Mendix runtime.
I believe these files should be removed after the xml import is done. I suggest filing a bug report if this isn't happening.
Edit: In fact, this was already solved in 3.0 and in 126.96.36.199, are you sure this is occurring in 188.8.131.52? Any release after the 14th of september should be fine.