I have been able to reproduce the bug with PNG having an alpha channel. Thanks for the very accurate description by the way, it helps a lot.
I'll try to find a way to fix it.

As far as I know the bug only exists for PNG files. If you have this problem with other formats, please let me know (Jim, your problem is with Ubooquity or with Calibre ?).

Bug reproduced on my side. I'll fix it before the next release.
Thanks for pointing it out !

Here is the promised test version.

The hostname can be forced using the new "-host" command line argument, e.g:

java -jar Ubooquity.jar -host 10.0.0.5

Let me know if it helps solving your problem.

Dual pages currently have no special treatment. So for them the display problem is more a lack of feature than a bug.

I'll resume investigating the problem asap, but I have planned to rewrite the online reader from scratch anyway.
So there will be a solution, either with a quick bug fix or (perhaps more likely) when the new online reader is ready.

I'll take a look at the lines you pasted first. Might take a while though...

A bit harder to do, but manageable. The feature is still quite far away though, as I have quite a few things to fix/develop first (and sooooo little time).

I'll work on it, but I can't say when it'll be done.