I assume you're talking about the voyager bit flip in the first part? It was just a single "bit" of data that caused that problem, a bit flip. The most likely cause is that of a cosmic ray hit on the chip holding that bit, causing it to switch. Had it actually been "reprogramed" showing a significant amount of its memory changing then it might have been something truly abnormal, but bit flips in spacecraft are not unusual. It's actually less common for Voyager because there's less solar radiation to contend with, which can also cause bit flips in near-earth (or at least, intrasolar system) satellites. It happened with Cassini just a matter of days ago:
[link to satelit.web.id]

The second part of your question I'm less sure of. Are you referring to the Japanese probe that flew by Venus instead of going into Venusian orbit?