Logical error with watermarks & thumbnails? (not a bug)

[Mikan]

Background:
Fresh install - PP 5.11
Enable watermarking of photos with overlay image? Yes
Thumbnail size 240 - midsize 480

Uploaded a couple (well, a total of 250..) of pictures .. evertyhing is fine: 480px picture looks fine and has that watermark "burned in". Thunbnail is 240 and without a watermark.

Now I decided that I want a little bit larger images so changed thumbnails from 240 to 260 and then "Scan database" and "Rebuild All Thumbnails" - all went fine except that now all those thumbnails have also watermarks(!).

Well... for me this is fine because actually I would like to have watermarks on thumbnails also but why when I originally uploded those pictures thumbnails they didn't have watermarks but when I changed their size and rebuilded them thumbnails have now watermarks?

[Michael P]

Because it's having to recreate the thumbnail from the original image which now has a thumbnail. The only way to prevent this would be to store an additional copy of the file as an "unwatermarked" version; but thats not pratical and we don't do that.