IR Remote codes that alternate?

I'm looking at the data output from a Thomson RCT110S remote and the
code is not consistent for the same button press. Instead it seems to
alternate between codes for each press of that button. i.e, press "1"
and I get one code, press "1" again and I get a different code, press
"1" a third time and it goes back to the first code I got. Occasionally
it will give me something else entirely and then go back to
alternating, crazy.
It does the same thing with both an IR receiver chip and a discrete
photo transistor, so it's not the receiver chip going wonky.

Another Thomson remote I have (RCT4130S) also does this.

But all my other remotes (Sony HT, no name DVD, aircon etc) all give a
single consistent code for the same button, as I'd expect.

Anyone know what on earth the Thomson remote is doing?

Thanks
Dave :)