Pascal,this is a known behavior with conditions.When you apply condition it just hide the extra rows and it does not impact the result row.So your result row actually shows the value irrespective of the condition you apply.
Now with the help of local functions like calculate result as summation you can show the correct sum after applying the condition but when you try to use that result in some calculation then it takes the original value thereby discarding the calculated value.
Same is happening in your case as well.Its taking the original value i.e 350 and not the calculated sum after condition i.e 270.
Hope this helps.
Regards,
AL