I think it's normal to see corrupt RDS when signal is weak (I get a similar effect on my home stereo if the aerial falls down). I think there is some (weak) checksum in the RDS stream, though, so the player should ignore corrupted strings once it's got a valid one... (does it?)

Something it could do is attempt to build up the text from successive corrupted strings - once you have three versions of the text, you can use a voting algorithm on each character to decide what (if anything) to display in that position.

BTW, it would be nice if it didn't restart the RadioText line everytime the text changes, but allow the old line to complete first. It's a bit irritating when the signal is poor and it keeps restarting.