iPad won't share tabs or history with other devices

The subject line refers to a problem I'm having with Safari on my iPad (3rd Gen., iOS 8.3) sharing its history and open tabs with Safari on my iPhone 4s (iOS 8.3), and Safari 8.03 on my iMac (Maverick).

Using my iPad, I can see the history of what I've done using Safari on the iMac and iPhone but none of what I've done on the iPad. Naturally, what I've done on the iPad does not show up in History on the iMac or iPhone. Similarly, while I can see tabs currently open on the iMac and iPhone on any of the three devices, I can only see open tabs on the iPad *on* the iPad -- i.e., I can't see them on the iMac or iPhone.

I'm logged into the same iCloud account on all three devices and Safari is switched "on" in the iCloud preferences. I restarted the iPad. I turned Safari "off" in iCloud prefs on the iPad. (When it asked what I wanted to do with Safari data synced with iCloud -- yeah, right -- I choose to keep it on the iPad. Then I turned it back "on" and no change on the iMac and iPhone.

Any suggestions?