npm update --save in npm@8.3.2 works differently to npm update in npm@6 when specifying an exact version

For example if you run npm install --save-exact cron@1.8.0

Then your package.json will look like this:

"cron": "1.8.0"

if you then run on npm@6
npm update

nothing is changed

but if you then run on npm@8.3.2

npm update --save

package.json is updated to

"cron": "^1.8.0"

and then if you run npm update --save again package.json is updated to

"cron": "^1.8.2"

This is doubly confusing as my pinned version is lost AND I get a different behavior if I run npm update twice

Originally posted by @matthewmayer in #2704 (comment)