Q: can't edit repeating calendar events

Once a week my granddaughters come to my place after school.  I've always put these days on my calendar as repeating events for the whole school year. 

Obviously things sometimes change in an arrangement like that, and sometimes we plan to do something special, so I add a couple of words beside the event's title to clue me in.  (for example, the repeating Event is Lizzy, then may sometimes edit to make it Lizzy, baking).

It's worked perfectly for years - till Yosemite.  Now, the edits disappear if I shut down the calendar.  About a week ago, it stopped doing that - the edits stayed, and I thought they must have quietly solved the issue...but now it's happening again, my edits are gone.

Is anyone else having a similar problem - or am is there a particular not-so-obvious way we're supposed to edit in Yosemite. 

The edits on NON-repeating events are fine - always stay.

I'd appreciate any help - I'm really not liking this calendar at all, for other reasons as well. 

Thanks,

Lynne