Reopened #374774:
"When making changes to an event or todo, KOrganizer doesn't recognize most changes - and thus doesn't let you save them. The "Apply" button remains disabled, and if you click "Okay", then your changes won't be saved. The following changes will not be recognized: 
 - changes to time and date
 - changes to recurrance settings of the event
 - changes to reminders

Recognized changes: 
 - category
 - check boxes "all day" and "blocks me for other events" (sry retranslated from German)

This means if you want your changes to take effect, you have to make changes to the category or one of the check boxes. 

An example: Say you have a task set as a reminder to return books to the library. You regularly repurpose this reminder depending on your due dates. Say this reminder was last set to go off on July 12th. Now you want to set it to August 15th. If you just change the date and press ok, your changes won't be saved. Your reminder will still be set to July 12th. 

Reproducible: Always

Steps to Reproduce:
1. Edit an existing task or event
2. Edit either one of time, date, reminders or recurrance settings
3. See if the "Apply" button is active or not, and check if your changes are saved when you press "Okay". 
Actual Results:  
Most changes aren't recognized and will not be saved, if you do not work around with additional changes that will be recognized by the program. 

Expected Results:  
All changes to an incidence should be recognized and saved. 

I haven't checked what happens to changes in attendants, comments or attachments (nor anything related to the journal editor), but it seems that anybody working on this bug will easily figure these things out anyway. 

I'm marking this as major because it seriously decapacitates me almost any time I change a task or event, and because it has a high risk of leading to data loss, and thus renders the program unreliable for anyone who is not aware of this bug. Of course the classification will be up to the maintainer. 

This happened with an ICAL calender (the default .kde4/share/apps/korganizer/std.ics location) and the default internal mysql akonadi backend. I had first noticed this bug in 4.8."

The bug is still present in v5.2.3.