svn1734 and prior svn 1717.
I had been using a custom png8 watermark which worked fine up to 1717.Decided to create new png24 image. Uploaded to zp-core/watermarks. Setting on the SIzed Image as cover 1%; offset h 95%; w 5%. Preview was fine, watermark was lower left corner.
Changed CSS for comment (unrelated) and refreshed screen. Not only did the watermark move back to top left corner, it was the previous watermark image which no longer exists in directory!
Cache cleared in browser before preview. reproduced several times.
Cached images will have the watermark already imprented on them. If you change the watermark image via the selection box--that is you pick a differently named image--the cache gets cleared so that watermarked images are re-cached with the new watermark.
If you just upload a new watermark, this does not happen, so you will need to manually clear your cache to see the results.