Panic bars

Does anyone have a reference for adjusting a panic bar on an exit door?
It's a glass entry door, with a Jackson Exit Device (the long bar that goes across the door, attached at each end to the door frame. You push down on the bar to exit.).
If I push the bar to exit, sometimes the bottom "peg" doesn't retract enough (or stay retracted), and it hits the threshold as the door closes. Strangely enough, if I open the door using the outside keyed lock, the "peg" does raise up high enough and the door will snick shut.
I tried the Jackson web site, but couldn't find any adjustment info.

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