For each directory and each file Easy2Sync, can check rules to see if this directory or file should be synchronized. Despite their name, negative lists are less restrictive and most of the time a better choice.
A typical mistake is to expect intelligence from the software when applying your rules (especially if you’re using positive lists). Easy2Sync exactly follows your rules but it can’t 'understand' them.
Now what does that mean?
Often, you want to synchronize a certain directory. This is normally configured corrected. But your rules may disallow the synchronization of the directory above. Result: Easy2Sync encounters the directory above and notices that the directory above may not be synchronized according to the rules. And thus it ignores the entire sub-tree, including the subdirectory for which you specified special rules.