Sorry I've never used the platform behavior - so this is all guesswork.
I guess that mirroring, flipping and making vectors negative then somewhere something is cancelling out the other ?
I will try to look and learn over the weekend - but I bet someone who uses platforms will be along with the answer before I can work it through.
Mind you platforms do look interesting ...and there is nothing on the TV...
Just had another thought - add in your player and pin it to this positional block. Where you were mirroring the block, mirror the player instead ?