When using Asynchronous printing, the controller attempts to treat the line as Shear-Only Line if there is only one other press and there are no gags. It does this by clearing the Part Queue on every halt. It also replaces the last part in the Print Queue when entering run. This allows the operator to set next and have it take effect immediately. However there were some holes in the logic that caused the print queue to get out of sync.

1. If the last part in the print queue had already been triggered by the sensor but not yet been cut off, entering the run mode queued another message for the part in progress.

2. Halting and restarting with more than one part in the print queue.

Both scenarios resulted in an extra part in the print queue. Eventually, with enough run cycles the print queue would fill up.

The logic for this was incorrect and was spread out over the code. The existing implementation was removed and replaced with a simpler one.

If the controller is operating in the simulated shear only mode:

1. When initializing the Part Queue, if there are messages in the Print Queue, replace the last Print Queue added with the first part in the Part Queue.
2. When initializing the Part Queue, if the printer sensor is blocked, the first part has already been printed on so don't add the first part in the Part Queue to the Print Queue.