It is impossible to use the browser's ctrl/command-z function, if I've typed content, and then switched between editing-modes (wikitext <-> visual editor) e.g. to preview.

Example problem, described by Sunrise on enwiki:

Since preview takes me to the VE, it can mess up the formatting when I go back to make more changes (e.g. generation of nowiki tags if I accidentally forget to close a ref tag). These changes can't be undone by Ctrl+Z, so I have to manually remove the tags or discard my edit.

In regular wiki pages, it is possible to ctrl-z to undo, after previewing, if I either:

• click back in my browser (and then accept the confirmation)
• use one of the ajax-preview gadgets