HTML5 introduced several new input types, several of which are specialized text inputs including email, number, url, search, and tel. These input types are not recognized by Page Should Contain Textfield, Page Should Not Contain Textfield, Textfield Should Contain, or Textfield Value Should Be.
The cause is that these keywords use the constraint 'text field' and ElementFinder will filter out any input elements that do not have type 'text'. Since these inputs are still text inputs, they should be treated as such. The number type may render a spinbox control in some browsers, but still behaves like a text-type input.

Here is a test that should pass, but fails with:
Value of text field 'name=email' should have been 'selenium@xxx.yyy' but was 'None'

Open Browser    http://www.the-art-of-web.com/html/html5-form-validation/   gc
Input Text  name=email  selenium@xxx.yyy
Textfield Value Should Be   name=email  selenium@xxx.yyy

With minor modifications to elementfinder, I was able to get the above to pass.

This is being entered as a result of this: http://stackoverflow.com/questions/34169390/how-to-find-value-of-email-field-using-selenium2library