Middle name questions (ESTA as well)...

The perils of having a middle name. This has been asked a few times, I have quite a generic name but a middle name to at least distinguish it. It's on my passport (some people seem to omit this on passport).
Anyway, the name of the ticket is without the middle name. I've flown on this sort of thing before, people don't seem to care much about that.
However, the Advance passenger information seems to want this, when I was filling it in last time, I added it. It then refused to find the booking after this using the name without middle and with, which wasn't that bad because in Upper so my seat selection was ok. Now I'm in PE, and champing at the bit on OLCI to get some extra legroom seats. So I'm wary of adding it.
I believe the ESTA doesn't need the middle name, I don't think it actually had a space for it. I didn't add one just now when applying. But wouldn't the Advance passenger information want to mimic the ESTA, which means virgin shouldn't be asking for it (and actually working if you do add it)?
Anyway, the name of the ticket is without the middle name. I've flown on this sort of thing before, people don't seem to care much about that.
However, the Advance passenger information seems to want this, when I was filling it in last time, I added it. It then refused to find the booking after this using the name without middle and with, which wasn't that bad because in Upper so my seat selection was ok. Now I'm in PE, and champing at the bit on OLCI to get some extra legroom seats. So I'm wary of adding it.
I believe the ESTA doesn't need the middle name, I don't think it actually had a space for it. I didn't add one just now when applying. But wouldn't the Advance passenger information want to mimic the ESTA, which means virgin shouldn't be asking for it (and actually working if you do add it)?