Exactly. The first few times I raised this with Garmin their response was, "That can't be happening." My response was: "OK--we have two contended hypotheses here. Either I'm an idiot or you're an idiot."
I've largely learned to ignore it which is fine when I'm on day rides but stinks when I'm on a multi-day ride and really need it. And previewing the route carefully after uploading doesn't help since it can corrupt it at any time.
Agree with you on MapSource. It is unconscionable that Garmin's software engineers took very common functions like dragging a route to a new road and made them require 3 or 4 times more clicks in Base Camp than MapSource. I just spent 20 minutes figuring out how to delete some service stations from old routes that lingering in Base Camp.
I'm not a big fan of Google Maps though. Just today I was trying to design a route and it would not let me draw it on a stretch of road that I've ridden or driven maybe 200 times as recently as last weekend (PA 641 west of Roxbury), but instead insisted on a detour.
I was seriously considering the Tom Tom Rider 2 but every review I've seen of it is terrible.