We had implemented this same thing about a year ago for one of my clients. We had a huge implementation we were doing and upgraded to 9.1.  We were told by Laserfiche that this aspect has been tightened down on.  They no longer allow the use of Dynamic Fields with the field property set to a drop list as of 9.1. It completely shut down one of my departments.  I did find a work around that works (allows use of list fields in QF in conjunction with dynamic fields in Laserfiche).  Since it was so catastrophic to this department we spoke with Laserfiche to help us after getting the department at least functional.  They approved what I implemented as one option they would have recommended. They were so greatly affected because we were using the list inside of Quick Fields for accuracy in pattern matching.  Let me know if you want further details to help.