Problem description: When user opens the item configuration form, the page scrollbar becomes hidden, but if the user opens the item test dialog, obtains a value, and then clicks on the obtained value to view the full value in a popup, the main page scrollbar reappears and becomes active while the value popup is still in focus. Once focus is removed from value popup the main page scrollbar becomes inactive.
Furthermore, when all dialogs are closed the page is thrown into the scrollbar position that was actual at the moment of opening the item form dialog:

Steps to reproduce:

1. Start server and agent
2. Open the list of items for Zabbix server host
3. Make sure that main scrollbar is present on the right side of the page
4. Open configuration form of any item that returns a multi-line value (for example "Get filesystems" item)
5. Make sure main scrollbar is not present on the right side of the page
6. Click on the "Test" - still no scrollbar
7. Click on "Get value and test" button - still no scrollbar
8. Click on the received value to open the value popup

Result: Scrollbar appears on the main page. It is active ang You can scroll the main page while the value dialog is in focus. Once the focus is removed, scrollbar becomes not interactable.
Expected: main page scrollbar should not appear when the value dialog is opened.