On WebGUI browser instance "browser1":

• login into user "user1"
• create calendar "test"
• set all permissions on calendar "test" to user "user2"
• create event "test1" on calendar "test" and add comment "test1"
• save

On WebGUI browser instance "browser2":

• login into user "user2"
• signin into calendar "test" of user "user1"
• open modification dialog of event "test1" on calender "test" of user "user1"
• add comment "test2"
• but do not save yet

On WebGUI browser instance "browser1":

• open modification dialog of event "test1" on calender "test"
• comment "test2" is not shown, as not saved yet
• add comment "test3"
• but do not save yet

On WebGui browser instance "browser2":

• save modified event "test1" with comment "test1 test2"

On WebGui browser instance "browser1":

• save modified event "test1" with comment "test1 test3"

On both browser instances "browser1" & "browser2":

• klick on event "test1"
• the bouble shows the comment "test1 test3"

--> Concurrent modifications of the same event by different users are overwritten silently.
"user1" is not been notified that "user2" already has modified event "test1".
Modifications made by "user2" are lost.