I currently have a Cisco Catalyst 2960-48TC-L switch that exhibits some strange behavior when I connected to the web based device manager (http://devicename or http://deviceipaddress). If I start a constant ping, as soon as I navigate to the web page and log in, the pings start timing out. They will continue to drop until I have closed the browser session. Traffic flowing through the switch doesn't seem to be affected (at least no one was complained yet), however it does cause havoc for my networking monitoring tool.
The switch is running SW version 12.2(52)SE.
Please note that telling me not to use the web manager because it "sucks" is a moot point, becuase I know. Management has dictated this be setup for the tier 1 folks to log in and make sure all the pretty lights are on.