Might be intended behaviour if that is the case it is not presented anywhere. Filter anywhere on pipeline seems to reserve some capacity or the line is wonky if having to sources merge.. Tested by swapping two lines between pumps but the problem switched too. Disconnecting the filter under the base, and simplifying route did not help. Might be affected by 2 liquid bridges.
Steps to Reproduce
Run the included save
This issue has not been confirmed by a developer yet.