Edit condition on a property causes values to be edited

EditCondition appears to edit the property. This is defined in MovieSceneSequencePlayer.h:

/** Start playback at the specified time */
UPROPERTY(EditAnywhere, BlueprintReadWrite, Category="Playback", meta=(Units=s, EditCondition="!bRandomStartTime"))
float StartTime;

When you break out the settings in blueprints, bRandomStartTime appears to be false but is actually true.