Why does searching by source not work sometimes?

This command does not work. index=grb_test sourcetype=QServiceManagerFormat | source="\\\\netapp4\\Quants\\ST\logs\\dailyTest20151020_152356rhbyvk\\qservicemanager.20151020.log" This one returns results: index=grb_test sourcetype=QServiceManagerFormat | where source="\\\\netapp4\\Quants\\ST\logs\\dailyTest20151020_152356rhbyvk\\qservicemanager.20151020.log" I cannot figure out a reason why. I've tried all manner of escaping the **source** field in the first search, but can't get it to work.