There are many bugs in the default A320.Even if you do a nice flight plan on WorldMap then, when you press “fly” , it gets modified when transferred to the MCDU.
There are other problems more important than this (IMO) for the success of the flight that have been discussed in the following thread.These issues are there for ages but they are not fixed at all.Wonder why .Are they unable to do that?
Default Airliners Lose Navigation Upon Reaching STAR - #104 by DBCooper8675