OSPF default information originate ALWAYS - eliminates default route being received

Hi guys -

I've been through Cisco articles and a fair amount of Google-fu, and still not certain what's caused this issue.

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I had 2 switches, A & B. Each were peering with another pair of switches over OSPF.

A peering with C & D; B peering with E & F.

All established fine. All receiving routes fine from their peers.

But A was not receiving a default-route (0.0.00) from C/D;

B was receiving 0/0 form E/F.

I did an examdiff and found that on A I had configured:
default-information originate always

whereas on B I simply had:
default-information originate.

I hadn't come across this always command before and assumed it was a typo on my part (indeed it was). But looking up what it actually does, it simply ensures that, even if the router doesn't have a default-route, it will still advertise one.

The only other command difference was to do with TACACS, so this seemed like I'd found my problem. I swapped to default-information originate and, hey presto, I started receiving 0/0 from C/D.

But I don't understand why this is the case, and Cisco's documentation doesn't help at all.

Can anyone please help me understand the root cause of the issue?

Thanks!