The problems and phenomena described in this thread are consistant with memory wear. Some may not want to believe it, but flash memory can tolerate only a finite number of write/read cycles.
This is a well known problem, not subject to debate. Frequencies are truly disappearing.
When rewriting from a program like Win500, bad memory locations are locked out and everything is fine for a while.
Additional write/read cycles can lead to information loss, requiring another total rewrite. The thing to do (short of replacing the flash memory- if that's possible), is to eliminate unnecessary write/read cycles.
Turning the scanner off and on requires a write/read cycle. Owners of base/mobile scanners can leave the scanner on all the time (I do this, although the degree to which it extends memory life may be minimal). For owners of portable scanners, leaving it on all the time may be difficult.
Memory testing requires read/write cycles and therefore is not a good idea. Memory is tested anyway (and bad sectors locked out) when a write is done. Additional memory testing only increases memory wear.
How long flash memory will last will depend on many factors. In many cases it will last as long as the device. Designers hope that it will. A certain amount of memory loss can be tolerated (everything will be fixed by a complete memory rewirite). We can hope that none of our scanners reaches the point that there is not enough good memory left.
Stop testing memory. It's destructive.
