I've not had this issue but then I don't print that often to our LPB6300 which is a CAPT device.
To check if it is a machine or driver/system issue, I suggest you open the Console application (Applications > Utilities) and check the CUPS page log. With Console open, you need to have all the logs showing down the left column so you may need to press the Show Log List button in the toolbar. Then expand the entry /var/log by clicking the triangle next to it. You then need to expand the cups entry and you will see page_log. Select it and every job that has been printed will be listed. Below is an example of my page log.
LBP6300 pahu 166 [20/Dec/2012:11:28:29 +1100] 1 1 - localhost Statement_Dec 2012.pdf A4 -
LBP6300 pahu 166 [20/Dec/2012:11:28:35 +1100] 2 1 - localhost Statement_Dec 2012.pdf A4 -
LBP6300 pahu 166 [20/Dec/2012:11:28:35 +1100] 3 1 - localhost Statement_Dec 2012.pdf A4 -
You can see two numbers after the date. The first is the page number and the second the copies number. For your print jobs that don't print the last page or two it would be worth checking if the page is shown as being sent and it is not printed, suggesting a machine issue, or if the page is not listed as being sent.
