Cannot get active document when user clicks the document in Adobe FM 2015.

I am facing the following problem:

I have a timer in my application that hits repeatedly after 2 seconds to get the active document name (if there is any).

If the user selects some text (on mouse click down) of the active document from Adobe FM 2015 then the following API call returns 0 (which is wrong):

F_ApiGetId(FV_SessionId, FV_SessionId, FP_ActiveDoc)

Later, if user leaves the mouse button (mouse click up) then in the next hit of the timer the document name will be fetched.

It seems that the Adobe FM 2015 cannot handle simultaneously both user input from the application and the API calls from my application.

Why is this happening?