The first thing we would need to know is what setup code are you using with the URC-6131 and what is the code that partially works on the URC-8811.

Next we need to verify that your learning technique is correct. When you do the learning procedure, are you holding the original remote button down until the 8811 gives the double flash indication that the process is complete?

Finally, have you looked up the setup code that you are using on the URC-6131 to see if it's listed on my site. Maybe there are advanced codes that you can use to program the arrow buttons. We could better advise you here if we know the 2 setup codes that you are using.