When you say you had "the pre-Dragonborn DLC patch installed before I went to Solstheim." Do you mean before you purchased and installed Dragonborn? It's not a matter of when you traveled to Solstheim via boat within the game, it's whether or not you had installed the patch put out in November BEFORE you purchased and installed Dragonborn.
I purchased and installed the Dragonborn DLC first. But, the boat to Solstheim at Windhelm did not appear until I downloaded the pre-Dragonborn DLC patch. So, really, I literally installed the latter
right after the former.
Of course, I know where you are going with this. And, absolutely not, I am not going to follow your instructions and redo the
many hours worth of gameplay which I have done in Solstheim. I should not have to.
I have a hard time believing that reversing the order of installation for these two items caused all of the bugs which I have experienced. In fact, deleting and reinstalling the Dragonborn DLC alone has cured all of the bugs which I have experienced thusfar, except this one.
Let's just face it--Bethesda released a very buggy DLC. It's their best DLC for TES5 yet, but, unfortunately, it's just annoyingly buggy.