Setting a shortcut key is not taking effect

Using DWCC 2018 10136 on Win10 I have set key F9 to Check Links Sitewide but despite restarting DW in does not do anything when I press F9.  I tried loading a Standard set of shortcut keys then switching to my set which I thought might cause my set to be re-loaded.  A previous answer in this forum helped me find the XML file where the shortcuts are stored and I attach a picture which clearly shows I have set the F9 key correctly.  I've no evidence but I'm sure I have found this on a number of occasions in the past where I have set a key and it hasn't taken effect. Is this a known bug?