When entering notes, ties are assumed to be placed forward. But if one note of a chord isn’t part of the tie, Dorico will tie backwards (even over several measures) to a previous instance of that note.
This is designed behaviour, and allows you to create a tie between non-contiguous notes, which is a rare but at times useful possibility.
I’ve noticed that behavior when I enter arpeggiated piano parts, and like it a lot. (Saves a lot of fussiness in the tieing, which also seems easier to read.)
Wouldn’t it make sense for the backwards tie not to work if there are rests intervening? Without rests I can see that it might be hard to guess what the composer’s intent is, but I can’t imagine wanting a tie over rests?
Easy enough to cut the wayward tie, and it’s not a very common thing.