Strange bug - "hidden dynamics" - difficult to explain

I noticed a split multirest in several parts of a piece I started from scratch in Dorico, There was a 7 bar multirest followed by a single bar rest. The single bar was empty, and I even “deleted” its content though there was only a bar rest on the affected instruments. Nothing was working, so I decided to add a bar and copy the content of that buggy bar into it. Once I did this, the instruments that had the split multirests displayed “floating” dynamics marking underneath the single bar rests. Once the faulty bar and those phantom rests were deleted, the parts displayed a proper 8 bar multirests. I know that I was copying and pasting dynamic marks from instrument to instrument, but I saw nothing unusual while I was doing so, and no dynamics appeared on those empty bars (and remember that also deleted the “content” of those empty bars to no avail). How those invisible rests were created is a mystery to me. Unfortunately, since there is no auto-backup, I no longer have a copy of the offending file before I corrected the issue. But I thought I should report it all the same.