I am still experiencing this with GNOME 3.20, I have filed a downstream bug report for my distro here: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1595684

*** Bug 756982 has been marked as a duplicate of this bug. ***

Created attachment 331041 [details] [review]
calendar: Do not overload :active to mark selected day

We currently use the :active pseudo class to mark the selected day
in the calendar. Whenever the selected date changes, the class is
added to the corresponding button and removed from all others.
However when the selected date doesn't change (i.e. when clicking
the already selected date), the buttons are not updated and the
use of the :active class conflicts with StButton's builtin handling
of the class - the class is removed on the button up event and the
button is deselected.
Fix this by simply using a different pseudo class.

Created attachment 331042 [details] [review]
calendar: Do not overload :active to mark selected day

SASS part of the patch.

Created attachment 331043 [details] [review]
calendar: Do not overload :active to mark selected day

Ooops, accidentally obsoleted the gnome-shell patch with the SASS one, reattaching ...

Review of attachment 331043 [details] [review]:

ok

Review of attachment 331042 [details] [review]:

++

Attachment 331042 [details] pushed as d184e5c - calendar: Do not overload :active to mark selected day
Attachment 331043 [details] pushed as d184e5c - calendar: Do not overload :active to mark selected day