Hi Saurabh,
I've seen that there are several issues with patch level 400 concerning SAP GUI for HTML - but I couldn't find out if it fits your situation.
Two days ago SAP released PL 410; see here http://service.sap.com/sap/support/notes/2098894
You can try this PL, if it solves your issue.
Another link covers regressions found in PL 410 http://service.sap.com/sap/support/notes/2316115
At the moment there are no regressions but this note will be updated in the future until a new PL is released.
br,
Peter