Interesting! OK, let me see if I can get that to work. I am not actually using kable. I am using a custom function that was written by @dcruvolo so not sure if this will do the trick. I didn't mention the custom function because I wanted to make my reproducible example as simple as possible, so I didn't want to have to put all that code in there too, but I never considered that it would be relevant...
BTW - you can see that function here: Create accessible HTML tables in RStudio?