I've flown quite a lot and I can't say that it has happened to me.
Sometimes what happens though, is that when you fly with an airline that is part of an alliance with another, when you buy a plane ticket through one airline, and their partner is actually running the plane, the flight will have 2 flight #'s.
Example: I flew from Toronto to Amsterdam buying the ticket from Northwest Airlines, the flight number they gave me was NW123 (example). However, Northwest doesn't operate to Europe, so their partner runs the planes that fly there (KLM Airlines), so on my ticket when i printed it out, said Flight # KL6789. At the airport, however, the display boards showed both flight numbers as: NW123/KL6789. In the end I still used the originial ticket that I bought and climbed on a KLM plane.
In the event of your plane cancelling, usually due to inclement weather, everyone is a little stranded, and they will often put you on a stand-by list on the next plane out by the same operator-- usually when you're traveling with kids, they will put you on a priority stand-by list. Flights cancelled due to weather usually are pretty bad and will most likely have to wait out the weather to really get any sense of what will go on. Acting frustrated with the staff will only annoy them, so if you want answers, be assertive but be polite.
One time I was flying from Newark to Detroit, but my particular flight was canceled but I was put on a different flight, not necessarily straight to Detroit but I had gotten on the next plane out to Cleveland and then onward to Detroit. As you can imagine if an entire flight is canceled, a whole plane's worth of passengers are temporarily stranded, so simply putting you on the "next" flight can be a little tough.
Continue checking your flights perhaps before you go to bed the night before your flight, or in the morning, and maybe check the local weather, make sure there isn't anything nasty coming along just to get a sense of what to possibly expect.
But to answer your question: I don't think they just arbitrarily cancel flights and rename them--- the only thing I can imagine is if the original aircraft is being swapped with another model to accomodate for capacity? I'm not sure what effect that does on an actual flight number. You should be fine, I'm sure what you experienced was just a hiccup on the airline's part.