Synchronization bug?

I'm finding some trouble with a simple collection-based synchronization. Here's the setup:

Sync collection (contains the following folders):
[ul]
[li]folder1
[ul][li] file1.txt[/li][/ul][/li]
[li] folder2
[ul][li] file2.txt[/li][/ul][/li][/ul]

Synchronize:
Source: coll://Sync collection
Destination: ...\Desktop\dest
Mode: one way copy
Compare: date (different) or sizes
Synchronize sub-folder contents
Ignore seconds when comparing by timestamp
Sync left-to-right
Hide unaffected files

The collection is on the left, dest folder on the right. The first sync work as expected. Then, I modify folder1\file1.txt, adding one character to the file, save the file, and press Compare. Dopus indicates there is nothing to sync. Am I missing something, or is this a bug?

Collections are not really support for Synchronize at the moment (the main reason is that collections don't support Flat View, which Synchronize relies on).

Thanks jon.