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Each time a collapsibleSet is initiated or refreshed, it removes the ui-corner-top and ui-corner-bottom classes from all containers in the current document having the ui-btn-inner class set.
The refresh function of the widget uses the jquery add() traversing function to find containers with the ui-btn-inner class set, to clean up the collapsible borders.
Coming back to a cached page shows then the "glowing corners" as described at #4002.
Suggestion for #4062: removing add() function which queries the whole…