This specific Mobile Safari (seemingly impossible and yet undocumented) problem kept me going for a long long time today, and I was just about to post a question about it he
Note: use commas as separators, not semicolons. The clean way are commas as separators. See the documentation page http://developer.apple.com/library/safari/#documentation/AppleApplications/Reference/SafariHTMLRef/Articles/MetaTags.html, they do use commas too. And at least Chrome shows errors in the console if you use semicolons. I know, that this does not affect iPad or safari, but if you can do it clean, why not? :)