How to avoid an endless loop between two fields where their On User Input affects the other?

How to avoid an endless loop between two fields where their On User Input affects the other?

Is there a way to avoid an endless loop in this situation?

Fields
  • Transaction_Date is standard date field
  • Transaction_QTR is dropdown with choices such as "2015-Q1", "2015-Q2", etc.

If user supplies the Date:  we supply the proper QTR.

  • I have a nice OnUserInput that calculates and supplies the proper Transaction_QTR choice.
    This works nicely by itself.

If user supplies the QTR:  we supply the approximate Date.

  • Unfortunately, with this in place, the result in an endless loop between the two (sorry!). :-/
    So of course I removed that OnUserInput.
Is there a way to avoid the endless loop?

(Agreed it is a rare situation, and fer sure not a business need, just a small convenience.)

Many thanks!