Can't type spaces in rich text field with slate editor

[davisagli]

Describe the bug
When using the slate editor to edit a rich text field, I am unable to type spaces at the beginning/end of a text node.

To Reproduce
Steps to reproduce the behavior:

1. Create a volto site.
2. Go to the Content Types control panel and add a new content type.
3. Edit the schema for the content type and add a Rich text field.
4. Start adding an instance of the content type. In the rich text field, try to type a sentence.

Expected behavior
Typing spaces should work.

Actual behavior
Hitting the spacebar does not add a space.

Software (please complete the following information):

• OS: Mac
• Browser: Firefox
• Volto Version: 16.3.0 (current master)
• Plone Version: 6.0.0rc1
• Plone REST API Version: 8.32.2

[davisagli]

@tiberiuichim @robgietema Any pointers where to look for this one?

[davisagli]

If I position the cursor in the middle of other existing non-space text, I can type a single space, but any subsequent spaces jump the cursor to the end of the field.

[tiberiuichim]

I'll take a look tomorrow.

[mauritsvanrees]

It is a problem on beta.plone.org as well, when adding a hotfix:
plone/plone.org#35 (comment)