What are the steps required to reproduce the bug?
- Go to a fieldable entities "Manage fields" page
- Start adding a new field by typing in text for a label consisting out of two or more words with a space
What behavior were you expecting?
When you start adding the label, a machine name is generated automatically as you type.
A space should be replaced by an underscore.
What happened instead?
While you type the label, the machine name is getting generated next to the label field, but the moment you add a space the machine name disappears, and if you want to save the new field, you get an error message, prompting you to manually adding a machine name