Yes, Default refresh not cancelling when you call refresh function inside before_refresh event. Executing default refresh first. 
I have another suggestion:
why you can’t re-create the data provider in correct order
I know, that is a pain, but it would avoid coding and fighting with default functionality.
There is utility available at BOB to copy the dataprovider within the report.
https://bobj-board.org/t/20948
Thanks 
Copy the dataprovider, in correct order
Use those variable into the report (all tabs)
Delete old data provider
Hope this would help
I will post if i found better solution
Shahubar Sadiq 
(BOB member since 2003-02-28)