Can iPhoto Libraries Swich between Connected Computers?

I’ve an iMac (10.5.8) and a MBA (10.6.8). Each has a iPhoto library. The one of the iMac is a big library, more than 9,000 images. The MBA has just a few hundred that I post or send on the road. The computers are connected via wifi, and the Pictures folders on each can be shared. Among the files in Pictures on each computer is its iPhoto Library, although I’ve never accessed the Libraries from the other computer.

The other day, when I opened the iPhoto Library on my iMac, up came the MBA Library. And then the MBA started having trouble because it reported that its start up disk was full. Sure enough the MBA iPhoto library was 7.29GBs. It had part or all of the iMac iPhoto Library. The libraries had switched. Seemingly on their own.

When I tried to switch to old library on iMac, I got warning that iPhoto library was locked. I had never locked any library. I unlocked it, but kept getting locked warning. Recovered iMac Library with TimeMachine. And physically deleted the MBA iPhoto library and emptied trash. Also for good measure, reduced size of MBA photo library.

So, I think everything is now OK. But what happen? And how? Losing 10 years’ images, even for just a few hours, was a scare.

Thanks in advance for help,

Armando