Moving away from the concatenation discussion, it happens to me all the time.

I've seen different combinations - First name with the initial added to the end (Jeffreyg), or first name and complete middle name added to the end.

I've only ever worried about air mile accumulation, not security/boarding pass, though. Never had an issue at checkin, security, or immigration - they seems to udnerstand that strangely enough some systems don't allow for middle names, and they get combined together. It does take them longer to check, but not seriously so.

As I mentioned, my only real concern is not having my boarding pass match up for EQMs, so I always double-check my account a few days after a trip.