Rigid Body Tools turns my object upside down!

Hope I have posted this in the right forum. I have a five letter logo (‘sweft’) and I have applied Rigid Body Tools to each of the letters. I have made each letter active and placed a plane to act as a slope and set this to passive. The simulation works fine, all five letters drop, hit my slope and roll down BUT the ‘w’ turns upside down the moment I start the simulator and I can’t for the life of me work out why. I have recalculated normals, applied visual transformation but it still seems to happen. Can anyone help me please? I’m sure it’s something straightforward I’m missing…Link to the blend file is here:

https://docs.google.com/file/d/0B2WqHg3IE2c6TmR0SEEyUFMzMG8/edit?usp=sharing

The objects have a negative scale


Select all the letters and Apply Scale and rotation (Ctrl+A / Rotation & Scale)

I knew it would be simple! Thank you for the speedy response.