Content Structure: Reusable blocks that aren't in the page are counted

[noisysocks]

Describe the bug
The Content Structure component mistakenly includes reusable blocks that aren't attached to the page in its Blocks count.

To Reproduce

1. Create a new post
2. Insert a block
3. Convert it to a reusable block
4. Click Content Structure
5. It reports that there are 2 blocks

Expected behavior
Content Structure should report that there is 1 block in the post.

Screenshots

[bph]

I agree the Block count is whacky, but I think it's not entirely related to reusable blocks. There might be something else going on.
I recorded two videos. The screen is bit slow moving but I didn't want to edit video, to preserve the full experience.

1. In the first video, you see me loading a post from the list of posts. Then immediately after the post fully loads, I look at the block count: 52. Also, note: 8 headings, 4 paragraphs, and 325 words.
2. Then I move a block upwards. The Block count is now 63. The block count increased, although I didn't add a block, just moved one. And notice the change in paragraphs? It displays now 6 paragraphs, instead of 4.
3. To double-check, I move another block, but the numbers don't change any more.
4. Let's see what happens when I add another Twitter Embed.: The word count increases by 1 to 326, Heading stays the same, paragraphs increases by two, and Block count increases by 12 to 75 blocks.
   (First video link http://recordit.co/v7g07SUjqO)

The second video was recorded right after the first one. Starting again with the list of posts.

1. Beginning count: Words 326, Headings 8, Paragraph back to 4 Block count 53, one more than in the first video as we added a block in between.
2. My intention is to removed the previously added tweet, but have a hard time to get the block toolbar to show. (Again be patient :-) Eventually, I succeed in removing it. And the immediate change in numbers: 326 words, 8 headings, Paragraph block increase by 2 and the block count by 10 (although, I just removed a block)
3. I saved the post and from the list of posts I open it again. The count is back to the orginal numbers. Words 325, Headings 8, paragraph 4 and 52 blocks.
   (Second video link: http://recordit.co/C03rtZhQF6)

Additional information:
Reusable blocks in total: 10
Reusable blocks used in this post: 1 block 2 times.

This happens on both browser in use:
Firefox Developer Edition 64.0b8 and
Google Chrome ersion 70.0.3538.102
On MacOS 10.13.6