Wikimedia Bugzilla is closed!

Go to http://www.opera.com/developer/opera-mini-simulator.
Run the java applet simulator.  
Enter 'wikipedia.org' in the URL box.  
The resulting page has a search box and a search button.  This is good.
Click the blue English link.  
URL changes to http://en.m.wikipedia.org/wiki/Main_page
The page shown has a menu button, an unlabeled Search box, and a Star button.
If you click on the search box, you will get a keyboard.
Enter whatever you want in the search box, but when you press ENTER, it reloads the Main_page.  

There is no way to submit the search form. It is impossible to search from this interface.

Searching from the original page is an effective workaround.