Jumbled URLs

I have a document which includes (among a lot of other stuff) about 30 URLs, each link attached to a shape. When I open the document and do a minor edit (not to any of the URLs), save and close it, I find on re-opening the document that a random selection of the URLs are randomly jumbled, i.e. http://abc.com might be substituted for http://xyz.com for a certain shape, while http://xyz.com remains correct for its intended shape.

Has anyone else had this problem?

(Note: the URLs above are samples only)