Shared Calendar Not Syncing on One Account

Hi guys,

I've got a bit of a weird problem whereby shared calendars aren't syncing for one of my users. Here's the situation:

Both myself and my wife have our own calendars, and we share our calendar to one another via Zimbra. We are both "managers" on each others calendar. So I've added my corporate Zimbra account to my phone (Galaxy S3), and I can see both my own calendar, and my wife's shared calendar - awesome.

However, when I add my wife's corporate account to her phone (also an S3), she can see her own calendar, but not my shared calendar. As I said, both permissions are exactly the same, there are absolutely no differences between the two, so I'm not really sure what's happening here. Any ideas guys?

Thanks,

Kev