Headline formatting cannot be removed in rare cases

### Steps to reproduce the behavior
In rare cases, formatting behaves weirdly and cannot be removed. It most often encountered this with headlines. I do not have reproduction steps for the issue, just a document that has the issue: https://www.notebook.ai/documents/125118

Removing the affected text and typing it new helps sometimes. However, in most cases, moving the text to an external plaintext editor, deleting the affected area (in this case the complete list and some text below), copying the text from the plaintext editor and formatting it from the beginning is the best bet.

### Expected behavior

Headline formatting should not occur without being removable.

### Actual behavior
In the following screenshot, the two last bullet points are to big:

According to the formatting bar, they are formatted as H2. However, the list entries' text does not look like H2.

When clicking H2 to remove the formatting, only the distance between the list items increases:

When clicking "remove formatting" instead of H2, the formatting switches to actual H2 text style:

Start with the linked Notebook.ai document and reproduce the H2 and remove-formatting interactions described in the issue, using the screenshots as the expected context. Trace the editor behavior responsible for list and headline formatting; done means affected list text can have its unintended headline formatting removed without changing spacing or converting it to an H2.

Written by the indexing model from the issue text.