Why did my basting sauce flop?
The reason that your basting sauce flopped was the recipe was calling for an emulision (basically, a vinegrette) and by leaving out the vinegar you are changing the one of the basic building blocks of the dish.  The sauce will require that you add the fats to the mustard as it will clump as experienced if you don't.  The mustard in the original recipe is used as an emuslifer and may need to be cut down without the addition of the vinegar.  To build a sauce like this, you should start with the vinegar, add the seasonings and any emulisfers (in this case, the mustard) and slowly drizzle the fats into the resulting mixture until all has been incorperated.  You will still get a smooth sauce as long as you keep the order even if you leave off an ingredient or two.