I've used Xcode's zombie debugger and managed to find this flag upon launch: 
This crashed the app, and re-recording from Instruments caused the same result. Relaunching the app from the device made the app launch without a crash and subsequent launches from Instruments resulted in normal operation without flags or crashes.
Can anyone make sense of this or advise? I'm getting a number of "heap corruption" crashes in production. The reports are limited to a handful of users, but I'm afraid that number is growing.
It looks like the Parse SDK's latest release notes (1.15.1) addresses this:
-Adds polygonal queries
-Fixes memory leaks related with PFCommandCache
But my crash reports are coming from builds with this SDK version.