Hoping this would get fixed in gw2014r2sp1, but doesn't look like it.
If you are in a multi-user calendar, use the nav bar to go back to your
mailbox, then use the nav bar to go *back* to the calendar, it doesn't
seem to put you back in the multi user calendar.

In windows 7, you need to click the option for multi user columns as
you get put back in the week view calendar. In windows 10 you don't
really even see a calendar (or you get your last used calendar, except
for multi user) and then have to click multi user columns to get back
into the multi user calendar.