Request to DAZ Vendors
Masterstroke
Posts: 2,479
Please, do not use "*.duf.png" for your thumbnails.
Use "*.png" instead.
The reason is, that I keep editing items and resaving them. Resaving overwrites the "*.duf.png" thumbnails. By having only the "*.png" ending, I could always keep the original thumbnail.

Comments
Oh exactly ! I couldn't agree more !
I almost do the same, sort of..., rename the files by using a Renamer ~ (Maybe or definitely I have OCD...)
For the record, please set: in DS > Preferences > Content tab > Thumbnail Saving > Use inclusive thumbnail extensions (*.png) - strict mode !
This is a Daz QA standard, so that there can be different images for tip and thumbnail - using only the larger tip images will impose an overhead on displaying files in content panes as the images need to be refreshed. As crosswind says, just adjust the saving preset so you don't overwrite the existing images