Same problem on DUDU7. Also, when new text appears, it is appended to the previous one, when it should be replaced.
Radio stations in Poland use RT to show the current song being played, latest news, etc., so RT changes every dozen seconds. 
FYI, in RDS there is RadioText A/B flag, and from RDS specification:
If the receiver detects a change in the flag (from binary "0” to binary "1” or vice-versa), then the whole Radio Text display shall be cleared and the newly received Radio Text message segments shall be written into the display; If the receiver detects no change in the flag, then the received text segments or characters shall be written into the existing displayed message and those segments or characters for which no update is received shall be left unchanged.
