ImageMagick messes up PATH

I have an installation created in InnoSetup which includes 
ImageMagick-6.5.0-0-Q8-windows-dll.exe that is executed in [RUN] 
section. My installation runs Python script in ssPostInstall which adds 
two entries in Environmental Variable PATH: "C:\Program 
Files\DMSSoftware\bin" and "C:\Program Files\DMSSoftware\lib". When I 
install my installation on a clean computer with XP Professional SP3 it 
only adds "C:\Program Files\DMSSoftware\lib" to PATH. When I repeat this 
but without ImageMagick (I deselect it in Select Task page) I get both 
entries properly added to PATH. I have checked my installation log and 
everything is as it should be so my guess is that installation of 
ImageMagick has something to with this. I have tested this a number of 
times even with new versions of Imagemagick and everytime it's the same.

Thanks in advance for your help,

Zlatko Lovcevic