Hi,
I have created a 5Gig NTFS Drive. Then installed cygwin on the freshly created drive. After that I compressed the Disk (NTFS compression). A short check with the Defraggler shows me "140% Fragmentation" - but I think I know what is "wrong". The now compressed Disk is filled with 2.2 Gig of compressed Data. But the "uncompressed" size of the Data is 3.2 Gig. In this case, nearly all files are fragmented - so 3.2 Gig of Fragmented Data is more then the complete used disk space 3.2 Gig fragmented (uncompressed) > 2.2 used Space (compressed).
I don't think this is a "Bug" but it is not nice - maybe you could fix it within the next release - better should be comparing the compressed sizes if it is possible to do so