Wiki: <<toc>> command doesn't work in edit/preview mode

I just created my first wiki here on BitBucket, and wanted to add 'Table of Contents' to one of my pages.
I inserted <<toc>> on the beginning of the document, and pushed 'Preview', but nothing happened.

The preview just displayed '<<toc>> ' on the top of the page.

When I saved the page, the 'TOC' was generated as expected.