Filter not working in a report!

Hi everyone.
I have a report, that is fairly simple, but I encountered a problem I cannot wrap my head around.
I have two DataItems (ex. Header and Line) which are linked (using ex. Var1, Var2, Var3).
Plus there is also a filter in Line DataItem property where variable ex. BoolVar=CONST(No).
I added a List in Report Designer where i added Group by using those same variables Var1, Var2, Var3.
In my list I added a table where I grouped data from Line on Line No.
I added Filter on List group to be BoolVar=FALSE.
But it doesn't work!
Can you say what could be the problem. I need to see only those Lines where BoolVar is TRUE.
Thanks in advance!