Race condition in GreenHopper code creates duplicate custom fields for "managed" fields

In certain conditions, an upgrade to GreenHopper 6.1.4 will cause two instances of a GreenHopper custom field to be created. For example, there may be two Sprint fields.

Note: this bug only relates to upgrading to 6.1.4 specifically. If these symptoms occur in prior versions of GreenHopper, we need to track them separately.