Is this a bug of the delegation option?

Description:

Trying the delegation option today I've got stuck into a thing where the option wasn't following my lead, so I'm open this to get sure if that's really consider a bug or not.

Expected Behavior:

The ajaxForm would normally work if any of the forms were removed and re-appended to DOM.

Actual behavior:

The delegation option doesn't obey to the jQuery selector and overwrite the forms that came before.

Versions:

jQuery: 3.3.1 and probably others; Browsers: Chrome and probably others.

Demonstration

Link to demonstration of issue in CodePen.

Steps to reproduce:

Just click on the buttons.