No alert message about non-saved changes in modal form is appearing, if any additional modal window was opened before.

Steps to reproduce: 

1. Open Data collection -> Maintenance
2. Click "Create maintenance period"
3. Add some data
4. Open any additional pop-up, for example Host groups "Select".
5. Close the pop-up
6. Click back or F5 to refresh the page.

Result:

No alert messages that changes will be lost, page is refreshed and/or return to previous page.

Expected:

Alert message with text "Changes you made may not be saved." should appear and page refreshed only after clicking "Leave".

Note! In Zabbix 6.0 there was only host modal form and this message appeared correctly, however, in 6.4 this problem is also persists in host modal forms.