Anyone use Drobocopy?

I just noticed it doesn’t copy some files which HAVE changed.

The report Drobocopy sent me details at least 5 files which are newer in the source than they are in the destination.

Does anyone know what algorithms are used to work out what is or is not copied? Even the file sizes were different - their dates too (source was newer than dest.)

Keen to know if anyone else uses it or has noticed any issues with it.