Actually, the reason this happens is that the gauge needle is operated by a small step motor. These motors will stay in their current position when power is removed, assuming there is not a load on the motor greater than the holding power of the internal magnets.
On another note, I installed an Optix gauge on my truck and noticed some erratic readings when I used my cell phone (Nextel). Upon contacting the manifacturer, they mentioned another person was having this same issue. Apparently the frequency Nextel phones operate on is very near the frequencies the step motor in the gauge responds to. I sent my gauge to them and a prototype replacement was sent in quick order. So far, the replacement is working properly. They are in the process of making a new batch of gauges and I am to receive one when they arrive. (The prototype they sent has a black face instead of the white face gauges I have. )
I suggest if anyone is having the same cell-phone related issue, contact Danin to discuss the problem with Eric. They are very helpful and my customer service experience with them has been great.
Andy