Disagree. If it is currently invalid to click the button, disable it, that is what it is for. Disabled buttons should be focusable, that resolves the issue with

Disagree. If it is currently invalid to click the button, disable it, that is what it is for. Disabled buttons should be focusable, that resolves the issue with disabling the focused button in response to a click. How you achieve this in any given environment is a different issue, if the out of the box disabled functionality does not work properly, you will have to find workarounds.