MK500 lost aiming pattern


1) 28th-Jun-2011  2) 1day 3) MK500  4) CE5.0 5) 2402822 MK500 Imager with last OS revision, Datawedge v3.3 with Auto Trigger set to ON, Presentaton set to OFF. After cca 10minutes the Aiming pattern dissapears while imager is still operational. The pattern does not reapear until device reboot. Is this known? It occurs on 3 of 10 devices. Thank you