Works here using 5.4.2 on 10.6.8 with the non-AppStore version. Perhaps you had OmniGraffle open when you pasted the necessary line into the Terminal app?
In the Terminal, do:
Code:
defaults read com.omnigroup.OmniGraffle
and make sure the line
Code:
UseOldBezierPathLayout = NO;
appears in the output.