It seems that you are having some issues with your Slingboxes since all of them show the same behavior and do not pick-up the duplicated commands.
As the first step, I recommend you to rest your Slingbox. This troubleshooting step will allow you to clear-out all the information about "old-data". If you do not know how to reset it, make sure to check this link:
Then, run the A/V source configuration and make sure to verify the positioning of the IR Blasters and if they are working in a proper way. Make sure to check this link:
Besides this, you can also test the available speeds in order to determine if this is the root cause for this unexpected behavior.
Finally, keep in mind that since the PACE STB model DCR 7111/03 is not included on the supported devices list, you might need to test some other similar model numbers in order to find an IR code that will allow you to control this device.
Hope this helps!