After disable and delete downloaded files (sequential) in tixati - it leaves parts that are at ends of those files.
As result - a bunch of quite big and unwanted dnd_file_crust_*.dat files... I don't think it is ok.
If I can delete the files without recheck so why can't I delete those parts too?

I believe I'm also experiencing this issue, where Tixati is retaining file crusts for files that are not selected for download. I think this is also related to how tixati shows stored bytes/file progress for removed files. To give an example, I have 204 file crusts stored for one torrent, and less than 100 files actually selected for download. Here's an example of what I'm seeing:

https://imgur.com/WinkMjl

Edit: I think I've found a workaround. If you have a torrent with "ghost data", i.e removed files that still show left over progress/bytes, then search for crust files that have your torrent base-16 hash in the name. Delete those files, then recheck the torrent. Any files that were set to "off" should now also show 0 bytes downloaded.

what OS and what version of tixati?

the files in your pic, were they ever allocated or downloading?

when you turned the files off, did you delete the files?

this is still happening. I've deleted the files and nothing bad happened. Even so, I like to keep a nicely organized download folder and this is just clogging it up