Touchscreen: wrong response

Good daytime.

I have bought 4700 and flashed Linux in it. In Opie I couldn't pass
calibration test because when it complete it starts again. In GPE test
passes, but records wrong results. So, for example, I can't press button
on screen because device do not respond correctly on touchscreen events.
In our (Russian) forum I knew that it appears not on all 4700 devices
(some units work properly).

So, I have some questions:

1) Does somebody met this problem and how it was solved (if was)?
2) If not, how I can check these "buggy" units in future?

Huge thanks and excuse me about my English :(

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best regards, Anzo