Most likely, the screen transition that is occurring following the logon is tripping-up Screensurfer's "keyboard lock" management.
Can you please start Screensurfer in diagnostic mode, (clear the log file) and reproduce this error, up to where you click on the ENTER for the logon screen-- don't do the refresh.
Then, send the file \screensurfer\hostserver\surfdiag.log to firstname.lastname@example.org.
Most likely, an event-driven screen template for your logon screen will fix this by setting the appropriate screen transition strategy. Logon screens frequently involve funky host buffers that can trip-up a modal environment such as an HTTP-based terminal emulation. We'll figure this out for you based on your surfdiag.log file, which we can use to simulate your situation using our "Toy Mainframe" TN3270 server in our labs.