Sorry, I hadn’t seen this before. It must be a problem with the autolayout, which sometimes seems like the computer has a mind of its own which doesn’t correspond to what a human would want. I am not sure why the dialog is only resizable in the vertical dimension. I will see about fixing this next week.
In the meantime, if you have caps lock down before you invoke the Edit Key command, then caps lock would be selected, even if you can’t see it, and similarly if you don’t have caps lock. Hopefully that is enough to be able to use it.
John