really often the modalpanels only appear after moving the mouse when the button is clicked.
sorry but can't get the problem
finally i found out what causes the problem.
we got an iframe on the page for displaying pdf documents. if there is no iframe, everything is ok. if the iframe is present, the click event fires only when the mousepointer leaves the button. i the mousepointer is moved on the button, also nothing happens
there was a tooltip with followmouse=true on it. this caused the problem....