LOL yah inline filters do that.... don't worry about it !
one time you ride it it will be 3/4 empty the next time it will be completely full
and the next empty again.... it don't matter !
it is strange you would think that if it does something once it will always do it the same way but fluid dynamics and random restrictions throw up so many veriables that no one can predict the outcome !
As long as it works don't worry about it look at it like it's only using 1/2 the filter when it's half full so it's saving ya money ! HAHAHAHA
....
Bob