Global variables, initial vs current value

I read up on a couple of similar (I think) problems, but they didn’t seem to be the same. Let’s see if I can include all the info needed first time round.
In my workspace, in environments, in globals I have defined a variable X-Jwt-Assertion.
By default, I have placed the value in the initial value column with nothing in the current value column.
According to the hover help on current value it says
“This value is used when sending a request. Current values are never synched to Postman’s servers. If left untouched, the current value automatically assumes the initial value
In the actual request, in the headers, I have defined the key as X-Jwt-Assertion and the value as {{X-Jwt-Assertion}}.
To my problem. If I copy paste the initial value for X-Jwt-Assertion from globals into the current value column there, all works fine. If I delete the contents of current value, I would expect (?) the value to be taken from the initial value (which is how I read the help text), but that never happens and X-Jwt-Assertion is sent in as all blank.

Am I doing something wrong, or …