Temperature Spikes on Heat Printbed

I have a problem. The temperature sensor appears to be affected by negative movement on any axis. As a result the temperature just spikes significantly. This causes the bed to stop heating and causes warping.

I have a Mendel Max 1.5 using a RAMPS 1.4. On other firmwares I don't seem to have this problem but with the Repetier firmware this happens. Attached is a screenshot of the Temperature Curve.

Looks like your moves cause a short in the thermistor. What you see are temperatures you get with 0 resistance. So my guess is that the thin cables at the thermistor are not well isolated and can touch each other depending on y move. Might also be an other place of the cable but this is the most critical place i think.

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