CSS Designer double-typing of numbers problem

I can't find anywhere on the forums where this problem has been reported. I may be wrong.

I am on MacOS with DW CC 2018 - when typing values into the CSS Designer immediately after choosing the unit, e.g. "px" results in a double typing of the first character. So for example, if I want to type 100px, I choose "px" from the drop-down, then immediate start typing "100" and I get "1100". This is very frustrating. It is not only on my machine. I have been training last week on 14 iMacs and every single one of them had this problem so it's not a one-off.

My CC apps are all completely up to date as of 18th Dec 2017.

Can anyone please help?