Runtime error after problem mass update

Steps to reproduce:

1. Turn on "Frontend messaging" in user settings (message timeout = 30s). Check in all boxes.
2. Create item and add trigger to it (trigger with Multiple problems, and manual close)
3. Create a lot of problems (dont know, something like 10-15-20). 
4. notification window appears. 
5. got to monitoring->problems
6. Then, close all problems with mass update. 
7. Press apply button in filter several times. in notification popup problems change status to resolved. 

Result:
Runtime error appears: 

 Undefined index: r_clock [zabbix.php:21 -> require_once() -> ZBase->run() -> ZBase->processRequest() -> CController->run() -> CControllerNotificationsGet->doAction() -> CControllerNotificationsGet->loadNotifications() -> CConfigFile->{closure}() in app/controllers/CControllerNotificationsGet.php:150]

Expected:
No runtime error