Preview copy paste format suddenly TIFF?

[laz232]

For work (reporting bugs etc when working on engineering software, documentation, discussing measurements) I have the following workflow:
screencapture
paste in Preview.app
markup
copy and paste into Mail.app

Pretty sure that this used to paste PNG files. Now it pastes TIFF, which is incompatible with a lot of customers /colleagues default email clients.

I have screen capture type set to PNG.

Am I going crazy or has something been changed in macOS - more importantly:
how to I ensure that copy/pasted graphics from Preview (which are PNGs to begin with) are pasted as PNG in Mail.app?

 

[Janichsan]

I followed the steps you described and also get a TIFF as mail attachment in Mojave. So this can't be that new.