[Pairoscope-help] grey bar in plot

[Yaping L. <lyp...@gm...>]

Hi guys,
What is the meaning of the grey bar in the following plot? I know grey means "Forward-Reverse" which should mean normal pair, but I did not use -n option, so these grey should not be printed out. Could someone tell me why it comes out? (Insert size too large? so it has not proper paired flag?)
And what is the longer bar mean? Does it mean that it have pair while shorter one do not have pair?
Thanks!