I'm sorry that at this time I don't have better details, as the crash reports frequently do not contain a mumble_ol DLL version numbers. Also, forum reports I've seen from customers are not incredibly detailed. I can inquire on the forums about the Mumble versions being used.
I have one crash dump with a mumble_ol.dll (not directly implicated in this particular crash) with a timestamp of "2-19-2011 2:44 PM" but I'm not sure if that's just a Windows file modification timestamp. MSVC reports the module info as follows:
mumble_ol.dll *C:\Program Files (x86)\Mumble\mumble_ol.dll N/A N/A No matching binary found. 63 0.00.0.0 2/19/2011 2:44 PM 6A430000-6A453000 CrashDump.mdmp: Native