In general I find the Xfinity boxes are sensitive to the code spacing. I create favorite channel macros and I need to adjust the timing between digits. I try to trim this to a minimum in order to create a remote that seems to execute commands swiftly, but this will burn me sometimes after Xfinity updates their boxes and changes the timing. In my case this results in skipped digits.

The boxes are also sensitive to stray IR. Check your RTI program to make sure that the handheld remote is not also issuing cable box IR commands that will hit the cable box along with the processor issued commands. This could cause the multiple digit response.

In the worst case, you may need to trim the spacing between repeats. This will be messy because you'll need to edit the codes.

If you have the RTI learner, it is nearly painless to start with an existing code set and generate a new code set by replacing all the codes using the native remote.