Interesting....I just tried a quick experiment. DCM's new preview feature and the thumbnail on the 'new uploads' page only work on cbz files, and seems to have problems with cbr's. I love the feature, and so tried to see if I could download a 'problem' file, recompile it and re-up it.
I did so with Treasure Chest v08 004. It was a cbr with some junk in it, doubtless for a Mac zip compiler. I dumped the files and created a new cbz.
The product was semi-successful. The file is now viewable in the preview feature, but interestingly, when looking at the first page, it reports it on the header as 'page 0 of 35'. All 36 images are visible, just numbered 0 - 35, rather than 1 - 36. Is this the reason that a thumbnail fails to appear on the 'Newest Comics' page?
AH! Before I could even post this, the problem fixed itself. Now a thumbnail is there.
BTW...my opinion only...I LOVE the format of the 'Newest Comics' page, and wish all pages were like that. I understand that render some titles that have over a hundred issues to be pages and pages of listings. But wouldn't it make finding the one you want 100% easier? Or alternately, how about a view that was like GCD's cover galleries? Then you could click on an image of cover and go to that issues' download page?
If it isn't an inconvenience on the admin end (cleaning out the older, non-preview compliant versions), I wouldn't be adverse to re-compiling & re-upping files when I encounter them. This way, you would eventually head toward having a site where the features work for all the offerings.