In the "normal" (full site) view of the Stack Exchange websites, the search field is pre-populated from the current context. E.g. the search field on https://stackoverflow.com/users/22656/jon-skeet is pre-populated with "user:22656", and the search field on https://stackoverflow.com/questions/tagged/c%2b%2b is pre-populated with "[c++]".
In the "mobile" view (for browsers on mobile devices), the search field is not pre-populated anymore:
(You can easily verify that by clicking on the "mobile" link at the bottom of any page.)
I am quite sure that in previous versions of the "mobile" view, the search field was pre-populated in the same way as it is in the "full site" view.
Is there a particular reason for this change? Could that feature be added again? I found it very convenient, e.g. when searching for an answer of a particular user.