What is a "zip bomb"?

Umm, no. Sorry.

I'm a paid, legitimate owner.

Free advice is worth what you paid for it?

I suggest do a Google search 'zip bomb" and read the results. Tells all about them! I confess I had never encountered the term and was intrigued to know more. Best wishes!

OK, I'll do that.

The important thing, though,  is that the Sophos product is aborting  scans,

and not telling the user about it.

I reported it because I thought/hoped the devs would 

a) care

b) have some insights.

So far, wrong on both counts.

Here's the short explanation:

A "Zip Bomb" is a zip file constructed in such a way such that decompressing it takes an inordinate amount of time and file storage.  When SAV encounters such a file, it generally aborts scanning that file after a predetermined amount of time, to prevent affecting performance too much.  I'm not sure why there's no GUI feedback on this (I'm sure the devs will see the thread and will add that item to their "to do" list).

In your case, Adobe Creative Suite 3 Design Premium 1.0.log.gz is a gzipped log file, and is probably quite large when unpacked.  The engine decided that it wasn't worth attempting to complete unpacking, so it threw an error and stopped scanning the file.  The result is that you have an archive that is unverified (it *could* contain something malicious).  I agree that the UI should alert you to this fact.

Thanks so much, Andrew!