New Site + Mac Outlook 2011, downloaded itineraries disappear

I know that's a really long subject, but I couldn't figure out how to say it more succinctly. I have had this issue before with Marriott's website and posted in that forum, but didn't find anyone else who had this issue. This same thing just started happening with the new Delta site (I've been off for a month, so I hadn't used it for work in a while). Here's what happens:

I book a flight with 2 legs, outbound and return. I go to my upcoming trips online, click details next to the new one, then click the calendar icon in the upper right, then select Outlook calendar. It opens with two links, one for the outbound and one for return. I download both of them, and they download as itinerary.vcs and itinerary (1).vcs. I open the first one in Outlook and save it, and it shows on my calendar. I open the second one and the first one vanishes from my calendar. I open the exact same invite on my windows PC (transfered via Google Drive, not re-downloaded), and both stay on my calendar. My Mac then syncs and the flight magically shows up on my calendar on my Mac.

I know, you're probably thinking, that sounds like an Outlook issue - and it probably is, but I never had this problem with the previous site. Does this happen to anyone else, or is my Mac just being a pain?

Thanks!