I had to add a rule to my data parser specifically to remove the extra :1, :2, :3… etc. from the end of FlightAware’s flight ID’s. I never figured out exactly what the pattern was, but, it was consistent for a few different flights (as in, some specific flights would always trigger the :x issue).
In any event, I’ve seen it too; it’s a bug that should be corrected on FlightAware’s end, but, should be something you can handle on your end too - just check to see if the second from last char in the ID is a “:”, if it is, truncate the last two chars of the ID and move along.