Setting a global variable in a pre-request script isn't working

I have a pre-request script on my collection, that sets a global variable value:

pm.globals.set("SOME-HEADER", headerVal);

I have a single request in this collection, and when I execute it, I can see the console log is outputting the correct value I expect.

However, the request has a header, and I am attempting to set this from the the global variable {{SOME-HEADER}} - however I can see that this is always set to the current value of the variable as shown in the variables UI. My pre-request script on the collection is seemingly setting it to a new value, but then then new value is not used on the request. What am I doing wrong?

Can you send a picture of pre-req. tab?
I have tried setting Header in pre req as a global var and then it was used in Headers with this value given in pre-req.

pm.globals.set("SOME-HEADER", "headerVal");

If you set up pre-req in Collection, Directory, Request places be sure that nothing along not save different value.

For me this is expected behavior.