Oof good catch! But yeah as Qiqi said, Lemmy doesn't actually delete the messages. It just gets marked as deleted. It's then up to apps to hide it accordingly. Should be an easy fix, thanks for the find :)
Additionally since you're getting a number of replications to each instance, consider them permanent. You can't guarantee another instance wasn't just set up to log.
Which thankfully means the future denizens of the Internet can have a full record of all the beans.
Yep, Thunder is checking for the deleted field in the comment thread but not in the reply modal. Will fix and try to get it in for the next nightly. As mentioned in another comment I made, Lemmy's API mark the comment deleted but still sends the contents.