set(plugin[get(thumbname)].onhover, showtext(get(scenetitle)) ) works only in flash version

To show hints on icon I use such lines:

copy(plugin[get(thumbname)].scenetitle, scene[get(i)].title);
set(plugin[get(thumbname)].onhover, showtext(get(scenetitle)) );
It works properly in flash version, but doesn't work in HTML5.
Does anybody know why?
Jan

Thanks for useful answer.
Jan