"ObjectSupportLib 1.2 installs a CFM-68K 'evnt' gestalt function where the Transition Vector is in the application heap. If two applications link to ObjectSupportLib, quitting the first application but leaving the second running will cause a crash when checking for the 'evnt' gestalt. This problem occurs on all 68K machines in our QA lab. If the gestalt function were in a detached classic 68K code resource (rather than in CFM-68K code) this problem would not occur."
Bottom line: The CFM-68K Runtime Enabler 4.0 package (which includes OSL 1.2), designed to fix crashing problems with previous versions, itself needs fixing. It looks like it's back to square one here (sigh). Again, this only affects 68K Macs.