Gutenberg: Spacer block breaks after importing page from another site

[luminuu]

Describe the bug
The spacer block breaks after importing a page (maybe post too) from another site to a new site using Gutenberg on both sites.
I have not tested this with posts, only with pages so far.

To Reproduce
Steps to reproduce the behavior:

1. Create a page on the first installation, add contents to it, including a spacer block somewhere. Save that page.
2. Export the pages via Tools -> Export.
3. Import the pages with the default WordPress Importer on the second installation.
4. Open the imported site, the spacer blocks are broken.

Expected behavior
Spacer blocks should work as on the original site.

Screenshots
Spacer block on the original page:

Spacer block on the imported page:

Spacer block on the original page, HTML view:

Resolving modal on the imported page:

Comparing a new spacer and the broken spacer, converted to HTML in the imported page:

Desktop (please complete the following information):

• OS: macOS 10.14 Mojave
• Browser: Firefox
• Version: 63

Smartphone (please complete the following information):
Not tested

Additional context
Gutenberg: 4.1.1
WordPress: 4.9.8

[ocean90]

Hello @luminuu, thanks for the report! This is caused by WordPress stripping any aria- attributes at the moment. This has been already fixed in core and will be part of WordPress 5.0.