The difference between how the Platform behaviour acts with solids and how it acts with Jumptrough, lays in the simple fact that Jumptroughs disable the Platform's 'Push-out-of-Solids' mechanism (under certain circumstances).
Short story: when the platform breaks trough the boundary's of a Jumptrough it will not push that object out of that solids polygons.
Your cat has frames with different sizes. As a result you have origins that wander and collision polygons that ramble.
The cat will, due the animating origins and polygons, dive into the solid for 1 pixel. Since it is a Jumptrough, it does not get pushed out.
Most people will tell you that the solution is a 'helper object'.
At 1 point, when you going to add non native moves to the platform behaviour, a 'helper object' will be part of this solution. But wandering origins and collision polygons will bring you even more problems, problems that you have not seen yet.
My suggestion: better take care of the animation frames.
https://www.dropbox.com/s/j5uhvq2g88hfx ... .capx?dl=0
Other suggestion: use a tilemap for the platforms.