When using Ctrl-X to cut and paste sprites, the sprite flags remain in the old sprite location. Maybe this is intentional? But it seems like maybe the sprite flags should reset back to a brand new, untouched sprite state when sprites are cut and then pasted elsewhere. Here's a GIF showing the behavior:

Yeah, I agree with MBoffin, this seems like incorrect behaviour to me. I might think differently if the flags weren't being copied over to the new location. In that case you could argue that cut/copy/paste deals with the image data only, ignoring flags. But the flags are copied so it seems like if you're going to cut some data, you should cut all of it, including flags.

This has been around as long as I've been using pico and a fix would be great

Thanks @MBoffin -- this is fixed for 0.2.5d. It was also happening when clearing a selection with backspace / del.