Did you send in a support ticket, as well? One of the ninjas mentioned working on a problem that sounds similar - he was going to respond and ask for some more information.
Can't be sure it'll help, but does the "Rebuild Database" item under the File menu on the second Mac cause those links to behave like the other attachments in the database?
If so, opening
this page in Safari on your iPhone may clear the problem up there, as well. Earlier this week, I had a few attachments that the iPad app would show but not open. I didn't think much of it at the time, but if the same thing happened to you, there may be something going on.
In any case, sorry for the trouble - if you get in touch with the support ninjas, we'd love to take a look at the database and see what's going on.