Could you confirm whether you have upgraded to R2 2018 SP1 (2018.2.710) This issue is resolved there. You can test this on our demos to confirm (video of the expected results is attached below): -ajax/searchbox/examples/programming/serverevents/defaultcs.aspx.
This seems to work fine in our demos. I am attaching here a short video that shows my testing steps and another one that shows how you can check the actual version used on the page. Could you confirm if you see 2018.2.710 Am I missing something in my test 153554b96e