Variable Not Passed Back Correctly

All the subs below take place in Module4. I have a variable, MoreDates, defined as Boolean. At first it was just dimmed, now I have it as Public. When it's passed to a sub, it's true; in the called sub it's changed to false (and I see it as false when stepping through) and sub is exited. The next line of the calling routine checks if true/false...but it's true again. I'm not passing by value, so I don't know why this is happening.

MoreDates=True
Do Until MoreDates = False
Query_BigCharts (MoreDates) '***************
If MoreDates Then
temprow = temprow + 1
Range("A" & temprow).Select
lastdate = DateAdd("m", -1, lastdate) ' backs last-written date up a month
Range("D6").Value = lastdate 'send to eom cell
lastdate = Range("D8").Value ' formula in d8 converts to last weekday of the month.
End If
If lastdate < FromDate Then
MoreDates = False
End If
Loop
End Sub.............