I've been using the platform movement a lot with the latest build and I haven't noticed any issues like that.
The only problem I've come across is when I put Platform behavior on my enemies they often don't report when they're squarely on the ground so they keep on showing their "falling" animation even when they're walking. It's on my list of bugs to report. I had to make a workaround with foot detectors to fix the issue.
If your character is falling through solids, make sure your solid objects are thick enough to detect when the character's speed gets really high.