To reproduce:

Create a record in the user_preferences table with:

"name": calendar_persistflt

"value": 0

If this value exists, the function get_user_preferences('calendar_persistflt', 0, $user) returns "0" (a String).

In calendar/lib.php, function "calendar_show_event_type(...)" there is a comparison like this:

if (get_user_preferences('calendar_persistflt', 0, $user) === 0) {

The "===" has as result false, because it is not true, that "0" === 0.

I changed it to "==" on our site and it seems to work so far.