Rounding errors when mimicking Mod() with FP()

[StephanP]

In an earlier thread, I've learned that modulo calculations are supported in CAS through the %% operator.
Still not quite familiar within the CAS environment, I tried the following in normal mode.

I've used the following to generate the subgroup H=<10> of G=Z13*
   

Which gave me the following results:
   

Starting x=2 on the Emulator and x=5 on the HP Prime, the list shows results with rounding errors.
This does not occur with the TI-84 or the Casio CG-20.