Nice one, now I'm waiting for the next release again...
Which I do anyway
In a test txtz file the image-link in index.txt was
!00003.jpg!
(i.e. not in sub-folder)
The image html markup was included in the epub, but the image wasn't 'added'.
If I explode epub, drag'n'drop the image into folder, then rebuild, the Image is included and shows properly in viewer.