Hi! I've been experiencing this "new dialogue-bug" since beta patch 1.7, already. I posted this some days ago, unfortunately in the wrong thread.
I have made a couple of tests since. To show that my "testing-methods" aren't that amateurish, this is going to be a bit more elaborate...

First, let me explain: We own two copies of Skyrim in our family, two different versions, both German versions, installed on two different computers. I have installed my version on different partitions of my system, one installation to play with (I am only playing with my own created mods, except for the HighResTexturePackFix) - the other solely for testing purposes, which is a fresh installed game without ANY mods and a clean script folder.
The first thing I noticed when I tried the 1.7 patch was, that custom topics of my mods, flagged as "SayOnce" reappeared, and that any custom topics I had made in my mods were highlighted as new. Once I reloaded that save, everything would work normally and "SayOnce" topics were gone. (However any edited vanilla-dialogue in scenes - which didn't work with version 1.6.89.0 - would now work just fine.)
So I tried to make a simple new plugin to test it out. I just made a little quest with a topic for Sven and Faendal in Riverwood. Switched two my clean installed Skyrim version and started a new game, of course without any mods. After finishing the Helgen-quest I saved and restarted, this time with my test-plugin enabled.
Arriving in Riverwood I found out that neither Faendal nor Sven had any topics of my Quest. I saved and reloaded, and guess what happened? All dialogue worked fine.
After that I changed that test-quest to not being game enabled but getting started via change location event. Strange enough, this time it worked perfect. As soon as I arrived in Riverwood the two topics were available, I didn't have to save and reload first.
Exactly the same things happened when I tried my test plugin on our second computer with the second Skyrim version.
I also found out that the game enabled quests do actually start (I made myself a debug notification on startup stage to verify that), just the quest dialogue won't get loaded for some odd reason.
At least for my two game versions, this new bug isn't random at all. It's absolutely reliable and replicable, though not really game breaking, as there are still workarounds and everything works just fine, once I reload any savegame which already includes the plugin. Needless to say that if I roll back to version 1.6.89.0 everything works normal, except for the "original" dialogue bug, of course.
So, maybe anyone else can confirm this, and sorry for my english.
