Found weird issue about Filter ribbon button in CRM 2011, if you browse any entity view, you can click on Filter ribbon button to activate or deactivate the filters on the column headings of view and you can sort out the records by column headings. This is standard out of the box (OOTB) functionality; it works for all system and custom entity views.
After we search something using Quick Find view, Filter ribbon gets disabled, not sure why it is getting disabled. For now I could not find any solution. Let me know if you have any solution to enable Filter ribbon button in Quick Find views.