Due to a series of bugs, CHDs created with CHDMAN versions prior to the one in 0.146u2 could differ between different OSs (XP vs Vista vs Win7 vs Linux vs Mac OS X), different service pack patchlevels, and even different PCs with the same software load. In almost all cases the SHA1s would match and the data and metadata should be safe, but if you attempted to join a torrent your files would not match. Additionally, there was a possibility of corrupt CD and GD-ROM CHDs being created.

For these reasons, you should re-convert all of your CHDs from the “old” v4 versions using the newest CHDMAN. Note that ClrMAMEPro and chdman -verify are unable to detect if your CHDs are problematic in this way, do not use them to determine if you may have the problems.

News Source: Here