Hi,
I am having the exact same problem!
I found that if you send a Vol - code before another code it works, (sort of except for HT Direct).

Would you be able to send me the hex codes that you learnt, as I only have the one variation for each command.

I have a feeling that you only need 2 variations, i.e you send out the first variation first, then the next time you send the same command, you use the second variation.