Immovable physics toggle problem

I've got a situation where I want to switch an object's physics between movable & immovable, however there's a problem with this as you can see in the capx. Click on the red sprite to toggle, & the sprite falls through the floor when it becomes movable (this gets worse with each click).

I've tried moving the sprite up 1 pixel before it's set to movable again to avoid overlaps, but that doesn't work. It seems to have no collision with the floor for a few frames. Any ideas for a workaround?

I would suggest this is a bug.

I posted this under bugs & Ashley confirmed that it's a limitation of the box2d engine. The same thing happens to a lesser extent with asm.js, so I'm still looking for a workaround. Any ideas?

Well i havent had much of a chance to take a look. You could always take a look at the Chipmunk Physics behavior which is here:

An update: I have tried the Chipmunk option and it works as you would expect. I dont know whether this is an option for your project.

Thanks, this sounds great. The post collision trigger stuff should add some interesting new possibilities over the current physics engine. Chipmunk's lack of tilemap support is a problem for me though, but I'm sure Rojohound will get that working in the future.