Issue Summary

Playing with tables on Confluence is always a great option to keep things in order. It is nice how we can easily copy and paste table content from a table into another one, which let the experience really great!
Though, we have to take care when copying determined types of content between tables, like the header row from a table to another one, as this makes Confluence reads that the table where we pasted it as if it has two headers.

Steps to Reproduce

1. Create a page and insert a table;
2. On the table header, type 1, 2, and 3 on each of the header cells;
3. Create another table under the current one;
4. At the header, insert A, B, and C;
5. Add more 20 table rows;
6. On the first table, copy its header (select it all until the row gets blue and copy it);
7. Paste it on the 10th row of the second table;
8. Publish the page;
9. Edit it and scroll the second table.

Expected Results

The content from the copied row gets pasted as a regular row, not a header
OR
The table supports multiple headers.

Actual Results

The table rows get broken - as much content you have in the table, worse the experience gets.

Workaround

After editing the page, in the issued table, remove and then re-add the header row.

This workaround must be applied every time we edit the page, as it is a momentaneously solution for each time you are editing the page.

You can also delete the pasted header row and manually add its content there, so the table will contain a single header and will work fine.
In order to identify which is the duplicated header, go to the affected page in the view mode and click over the ellipses > Page Source - navigate to the broken table and identify which table row has the text highlighted with a gray background-color - in case the entire row is grey, then it is probably also the second header.