Datalink 2013, Calculated Data Time Interval and Filter Expression

I am using datalink 2013.  I have calculated data with a filter expression but leaving the time interval blank.

When I apply it, it seems to work fine.  However, if I go back and click on it again...it puts the text from the "Filter Expression" box INTO the "Time Interval" box..which is supposed to be blank (I only want a summary for the whole time period).  If I then hit apply, it gives me an error that the time interval is not correct (which is true since it is a reference to a cell that has my filter expression in it).

Not sure if this is making sense and I am not on the computer right now that I can do a screen shot.

Anyone seen this before?

Thanks.