Winch bug?

Hello guys, I have been working on a aerial tramway in one of my ‘creative worlds’. The tramway is hung on a monorail track and connected to the upper stop with a winch (I could use thrusters but I want realism). However, during the rolldown, the cabin just randomly stops close to the upper stop. The winch cable is not tensioned, it even hangs below the cabin. If i remove the winch, the cabin immediately starts rolling again, so it has to do with the winch.
Here’s a screen to show what I mean.
http://img822.imageshack.us/img822/3334/gmflatgrass0000sb.jpg

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