Steps to reproduce:

Scenario #1 - two clicks are required to confirm / cancel the action and close the pop-up

1. Open Data collection -> Hosts
2. Click on Items / Triggers / Graphs for any available host
3. Check the checkbox for any of the rows
4. Click copy button under the list of available items
5. Click on select button for any of the options (Template groups, Host groups, Templates, Hosts)
6. Close the list (use close or cancel button)
7. Close the Copy window (use close or cancel button)
8. Check the checkbox for any of the rows
9. Click on any button, that requires confirmation, for example Disable
10. Click Ok or Cancel on the appeared pop-up window

Scenario #2 - multiple clicks are required to confirm / cancel the action and close the pop-up

1. Open Data collection -> Hosts
2. Click on Items / Triggers / Graphs for any available host
3. Check the checkbox for any of the rows
4. Click copy button under the list of available items
5. Click on select button for any of the options, for example Hosts
6. Select the host that is already assigned to the same item
7. Close the Copy window (use close or cancel button)
8. Click Copy
9. Close the window by clicking Close or Cancel
10. Check the checkbox for any of the row
11. Click on any button, that requires confirmation, for example Disable
12. Click Ok or Cancel on the appeared pop-up window

Result:
Scenario #1: At least two clicks are required to confirm the action and close the pop-up window
See video:

Scenario #2: Multiple clicks are required to confirm the action and close pop-up

Reproducible on different browsers.

Note: issue disappears after reloading the page

Expected:
For both scenarios: action should be confirmed on the single click, pop-up message should be closed