List of steps to reproduce

• Open WikiEditor (editing any page with 2010 wikitext editor).
• In toolbar, click on Advanced > Table button. “Insert table” dialog opens.
• Uncheck “Add header row”.

What happens?:
In Example preview, header row is replaced with a classical row. So you see a table with 4 rows. But if you press Insert button, a table with only 3 rows is generated in wikitext.

What should have happened instead?:
The header row should be removed, so only 3 rows are displayed in the preview, to be consistent with generated wikitext.

Note:
If you change row count, the example remains: this is not a real preview. However the user should understand that checking “Add header row“ adds an extra row which is not included in row count parameter.