What a horrible failure mode! Kudos to the OP for even thinking to investigate this.
The mentioned memtest86 tool sounds quite useful - so useful, in fact, that it seems it should be part of the operating system. If my OS is perfectly willing to write corrupted memory back to disk, and it's designed to run on thousands of different OEM hardware configurations that may or may not have ECC RAM, then I would expect it to proactively monitor for faulty RAM and bitflips.
Is there a good reason why this isn't the default behavior of operating systems (maybe it is - I use Mac and don't know much about Windows)? It seems like a trivial diagnostic tool that could prevent a lot of headache. But perhaps the problem is there's no reliable test without some number of false positives, so popping a warning on the screen that your RAM appears unhealthy seems like a good way to confuse the average user. But then again, so does silently corrupting a video file.