I asked a question about a game I'm working on. It involved a ship attaching to a block via a physics joint. The problem was, when you thrust up the screen with the block attached, the block moved gradually closer to the ship until it eventually was above it.
User R0j0hound mentioned it could be a bug with the physics joints. He's far more clued up than I am with the technical side of things, so just in case it is a bug, I'm posting it here.
R0j0hounds reply t looks like it's a bug with joints. I landed on a higher ledge and the orange box just sat above the rocket like you said. The joint offsets aren't the same at different positions.
Here's a demo of the CAPX showing what I mean. Move the ship above the block, then thrust up the screen and you'll see the problem.
AMD 645 Athlon X4 Black Edition
Nvidia 560 ti graphics card
Windows 7 64
Google Chrome Version 23.0.1271.40 beta-m (have tried with none beta version too and IE9)
And here's the CAPX so you can have a proper look at what's going one.
EDIT just added system specs and browser info etc.