I downloaded from online and installed the August 13 TNAP 4.1 image. All images loaded prior to this did not solve my clock issue when I switched my Mio+ to standby. My Mio+ clock has always been accurate if I left the receiver powered. However, this latest release may be the magic bullet. So far, the clock is remaining correct even in standby. I will continue leaving the receiver in standby whenever I am not using it to test if it remains accurate.
Added: This morning I installed the new August 15 image. Continuing to monitor.