Hi,
I hope you have created the CMOD on top on CALMONTH with default values pops up when you open the bex query in RSRT & BEx Analyzer. But when you incorporate the query in dashboard it doesn't pops up current month did you noticed that, you might have passed the DEC2015 as value before proceeding so every-time you run the dashboard it takes the value.
Create the BEx variable on top on Calmonth as optional and when its passed empty it should take current month, else it should consider user input. Now you pass the input as blank while creating the dashboard. Hope you got my point.