In Service Portal landing page, when 'IT Request Something' option is clicked, it opens up Service Catalog home page where an additional search box appears. This issue is observed after upgrading to Quebec.
The 'sc_landing' page -> /sp_page.do?sys_id=53261e3487100300e0ef0cf888cb0b7c contains two 'Catalog Homepage Search' widgets included under 'Service Catalog - Container 1' ie
[ OOB -> 'Catalog Homepage Search' & Custom one -> 'Catalog Homepage Search v2'] because of which two search box appears.
To fix the issue go to the sc_landing page -> /sp_page.do?sys_id=53261e3487100300e0ef0cf888cb0b7c. Then edit this page in Page Designer and ensure it includes only one 'Catalog Homepage Search' widget, preferably the OOB one.