sonar X2 piano roll problem.

hi guys, my english is limited, so ill try to explain. i hope u will still understand:
 
when i open the piano roll to work on midi notes, sometimes when i zoom just a lil and i play my song, i lose my "bar line".
You know the bar who go left to right when playing. the piano roll stay at the same place but i keep losing my bar line who disapeared at the right.  
the only way to fix that is to reopen the piano roll each time. cmon thats so boring lol 
is there a way to fix it more quickly than that ? tx