This behavior showed also on Crome before I banished it. (Chrome's default text was identical) Support at my usual webhost has been looking at the problem for two weeks without result. Today I loaded the same code to a different host organization (under http://waggledance.us) and I'm seeing the same default behavior, including an occurrence of the "first time okay" observation.
      I note there is a default "Main.css" on that second server, which makes me ask whether a default .css is getting slammed on my user after <my-custom>.css serves (on both hosts??).

My stylesheet mouseover/hover texts show properly when <my-custom>.css comes from local (offline) disc, but when online, a default "Control+R improves the quality of this image..." shows instead, presumably from the browser. Occasionally a test will show my custom hover text on the very FIRST mousover event ONLY, then the default kicks in. This behavior showed also on Crome before I banished it. (Chrome's default text was identical) Support at my usual webhost has been looking at the problem for two weeks without result. Today I loaded the same code to a different host organization (under http://waggledance.us) and I'm seeing the same default behavior, including an occurrence of the "first time okay" observation. I note there is a default "Main.css" on that second server, which makes me ask whether a default .css is getting slammed on my user after <my-custom>.css serves (on both hosts??).