Another update...

I managed to get access to a PC which has a COM port so was able to connect my original Pronto RU940 it. And hey presto, it learnt every code off the BDP-LX55 remote absolutely fine and all the codes work too.

So as Lyndel mentioned, the original Prontos seem to be brilliant for learning codes where as the others (from my experience) don't seem to be much good.

And as an added bonus I found that my broken Pronto RU890 (they aren't compatible with beer apparently!!) still is able to learn codes straight into ProntoEdit so I have that as a learning backup.