Hi, the way the Lieca shutter is designed takes care of the 'uneven' exposure. Basically the gap of the shutter increases slightly as it runs off, thereby increasing exposure - this is because the shutter blinds accelerate from a standing start so are travelling faster when the reach the other side of the frame, and if the gap remained the same, under exposure of the last part of the negative would occur.. If you take the back off the camera and slowly wind the shutter, you will see the opening curtain capping increases as the shutter is wound.
The Contax, on the other hand, does not need this feature as the blinds run vertically and the difference in exposure is comparatively much less and can be tolerated.

Hope this helps,