Text is deleted when undoing a hard break inserted into a heading

[sarahmonster]

Typing a hard return (Enter) in the middle of a heading, then using command+z to undo deletes everything that appeared after the line break:

Typing command+z a second time brings the text back.

Using the backspace key instead of command+z undos the line break in the way I'd expect.

I would expect that typing command-z at this stage would just undo the line break I'd inserted, rather than removing the second paragraph entirely. I'm not certain if this is a bug or expected behaviour—I suspect on a technical level, it's undoing the "create new block" first and then the "break heading", but from a ux perspective, it feels unexpected.

To reproduce:

1. Create a heading.
2. Type a hard return (enter) in the middle of that heading, breaking the heading into a heading and a paragraph.
3. Type command+z.
4. The paragraph of text disappears.
5. Type command+z again to bring the deleted text back.

[carladoria]

I was able to reproduce this. It seems to only happen with headings. With text blocks, using command+z will revert the action of the broken line (2 blocks created) without deleting the text.

[mrwweb]

I just tested this behavior in a list and found something very similar. In that case it deleted both list items:

This feels related-ish to #11165.

Win 10, Firefox 63, WP 5.0-beta1-43832

[earnjam]

Paragraph duplicates the portion moved on the first undo, then removes the new block on the 2nd undo.

This gif compares header and paragraph blocks using these keyboard steps:

1. return
2. cmd + z
3. cmd + z

I'm using OS X, Chrome 70, WP 4.9.8 and latest from Gutenberg master

[earnjam]

Related: #8882

List block seems to restore correctly with a single Undo (likely because the return doesn't create a new block), however the cursor gets placed at the end of the line after an undo.

[ellatrix]

Duplicate of #8882.