I believe this was introduced in 1.8rc2. With Toggle, when specifying the (optional) Speed as a string (not a number), but the (optional) Options are NOT specified, the effect is showing but then quickly hiding the item being toggled.

Using the sample code at http://jqueryui.com/demos/toggle/ - the line under "//run the effect"

Works:

1. $("#effect").toggle(selectedEffect,options,500); //default example
2. $("#effect").toggle(selectedEffect,500);
   
3. $("#effect").toggle(selectedEffect,{},"normal");

Does NOT work:

1. $("#effect").toggle(selectedEffect,"normal");
2. $("#effect").toggle(selectedEffect,"slow");