Note: This might apply to DSE on the Mac too, I'm not sure.
When you're trying to determine a storyform it is often incredibly advantageous to use the multi-select capability of the Query System windows (the Theme Storyforming area is often best). I usually do the initial easier work in the Story Engine Settings and Theme Browser, but once I get uncertain the multi-selection becomes important.
So here's the tip -- be careful about getting down to one storyform. I find that if you have some items multi-selected, like say OS Problem options of Process, Proven, and Trust, and then you make a selection in another area that gets you down to one storyform, you can't go back to your multi-selections after getting getting down to 1 storyform. e.g. going back to OS Problem you only see Process now. (At least that's what I've found.)
So the solution is simply to leave something like Story Driver or Story Limit unselected. I think Story Limit is the best, it seems to affect the other things the least -- I'm not even sure if it affects signposts. Then once you're sure enough about your storyform and don't need to go back to your multi-selections, you can set the Story Limit then.
Hope that helps!