Yeah this is one of the quirks you'll have to deal with. Is this a solid or a jumpthrough platform? Either way the platform behavior has a bunch of quirks like this which aren't exactly fixable, because it works perfectly for project A but not for project B and fixing it for project B breaks project A.
In a way it even makes sense, the character steps off the platform, but the platform moves under the character before it can fall. Maybe you could try to add the platforms velocityX to the character when it steps off so the character sort of gets flung off at the same speed the platform moves, so the platform can't catch up to the character anymore?