I have encountered this sort of stuff a lot of times. It is pretty damn confusing and quite frustrating to solve.

This most probably seems to be a grounding problem ..... or maybe a loose contact. Has anybody considered the possibility that the "finger on the plastic" provides just enough pressure on the device to ensure proper contact??? :D

But as far as my limited experience goes, it has been mostly wasted in solving useless problems like this, and I believe the trouble is with some physical/design aspect of the PCB. Check the connectivity and gound to begin with.

Or if you are a software engineer, find something that works as well as your finger and paste it to the chip... :))

kundi