I registered today using the same openid as for all my other stackexchange accounts, but I did not get the usual 100 rep for linking accounts. Is it a bug, did I do something wrong or am I missing something?
We had a bug between sometime last night, and around mid day today that was causing association bonus to not be assigned (under some cases).
The fix for affected users is simple, clear you associations and then re-associate.
I've already done this for your accounts (your meta rep will sync with time, but your Math.SE rep is already correct).