Date range prompt doesn't show range when report is run

[ej]

Sometimes when I create a prompt and specify that it is to have a range, everything looks fine until I run the report.  Then the prompt only appears with a single select, in this case, a single calendar instead of two calendars.  I've not been able to tie it to anything specific, although I suspect it may have to do with the underlying model.  Does anyone know the why of this behavior?  It is frustrating when you think you have a solution to a reporting issue and can't get the range prompt to function as expected. 

[ej]

Well, I figured out the answer to my own question.  My filter was using '=' instead of 'in_range'.  Silly me.