iCloud won't send shared calendar invitation

Short version:

An iCloud calendar won't share from my Apple ID/iCloud#1 to Apple ID/iCloud#2. BUT I can get iCloud#2 to share a calendar to iCloud#1, so I know how to do it. Conclusion: my iCloud#1 isn't behaving properly.

Long version:

I want to share an iCloud calendar from Apple ID/iCloud#1 to Apple ID/iCloud#2. I followed the instructions here: iCloud: Share a calendar with others. It's not happening. I tried over and over; nothing.

It won't send an invitation, and it won't save with whom I want to share it. (when I click the share button to check, it never remembers the email address I typed before):

(from iCloud.com)

I tried this: iCloud: If you’re not receiving event and shared calendar notifications (though I think the problem is with Cloud#1 not sending) I tried all combinations on both accounts.

To check if I'm doing it right, I tried sharing a different iCloud calendar from iCloud#2, and it worked easy peasy. So I know how to do it correctly, it's just not working on iCloud#1.

I have tried from my desktop iMac (running the latest Yosemite), my iPhone (current iOS), and on iCloud.com.

Apple ID/iCloud#1 is really old, could that have something to do with it? Apple ID/iCloud#2 is about 1 year old.

Unneccessary Details:

iCloud#1 is my person account, iCloud#2 is work. I want my personal calendar to reside on my personal iCloud#1. I know a workaround: put my personal calendar on my work iCloud#2 and it will share it with iCloud#1 and it will work. BUT I just really want to get this working properly in case I don't work here one day.

I'd post this to a Calendars community, but I don't see one. Please let me know if I should post someplace else. Many thanks!