I played around a bit tonight and found that it seems to be linked to the number of total dialogs present on the map, which of course is my good friend the dialog overflow that was supposedly fixed yonks ago. BUT, if the dialog is linked to an object, it doesn't randomly fire at the end of the first map objective, but properly when the object is activated. All dialogs -- past whatever threshold that I have no real way of calculating -- set to visible on a map objective or a dialog button will fire upon the completion of the FIRST map objective. it seems to be a sort of FIFO thing, since it's only the dialog that caused the initial problem and the new one that I added to test that exibit this behavior.
I've put in another bug report. Is there any way of knowing whether this will even be looked at, short of Zero coming in and saying so? I'd like to know what the chances of a fix are before I spend a few weeks taking a hatchet to a very complex map.
I wouldn't hold your breath about the Objective Complete Dialogue bug being fixed. It's been a problem for more than 6 months now. Just switch to using component complete, if possible. You can trigger it off of a component that is also an objective and it won't occur until the objective occurs.