For everyone who already stumbled upon this bug (Typesetter 5.1 only):

When certain nested (wrapper) section structures are copied to the Section Clipboard, they will be messed up after pasting and reloading.

This commit fixes the bug.

If you don't want to wait for 5.1.1, patch your current Typesetter 5.1 setup …

• Either get the fixed Edit.php file from GitHub and overwrite the one in [your Typesetter installation]/include/Page/Edit.php with the new one
• Or download the whole current master ZIP from GitHub and overwrite [your Typesetter installation]/include/Page/Edit.php with /Typesetter-master/include/Page/Edit.php extracted from the ZIP