The controller tries to minimize the times when it needs to preserve the part queue when the controller is halted. For example, if the controller has one press and one gag. If it has no tools defined to use the gag there is no reason to maintain the queue when halting.

In the above example there is one reason the controller may need to preserve the queue and that is if there is a stitch gag defined and there are stitched parts in the part queue. The controller had a test to detect the stitched parts but it was implemented incorrectly and failed accurately detect them. This has been fixed.