1. Navigate to data:text/html,<div> 2. Open inspector 3. Switch to elements panel 4. Double-click on <div> 5. Start entering attribute name/value, e.g. id="1" 6. Observe that the text being types also appears in closing tag 7. Press enter 8. Observe that attribute/value is replaced with empty active edit box 9. Enter attrbiute/value again 10. Press enter. Now it works.
This workflow means that you're editing the tag name rather than its attributes, which leads to the confusing behavior you've noted. One way of solving the problem would be to make the spacebar behave the same way as tab for this field. I'm not sure that's the best solution, but it looks pretty straightforward. I'll upload a strawman patch, and if it's something we're happy with, I'll try to figure out how to test it. :)
I thought it was pretty obvious here that you're editing the tag name and not an attribute. When you're on the tagname, you can just tab to start editing an attribute. In the past we made this more clear so that when you hovered the tag, a clickable "..." region showed up in a new attribute spot which you could click to immediately start creating a new attribute. That later got removed in favor of the current behavior. Is the current behavior really that confusing?