this problem is due to the fact that there is no height specified for the div of the main container of the business process flow. When the optionSet opens, it overlaps the main container height size. The solution for this problem is to set the height of the main business process flow div (div with id "processStepsContainer"). I suggest you create a Web Resources that is a Style Sheet(CSS) and that sets this:
#processStepsContainer{ height: 200px; }
Then you just need to use a link on this style. You can do it using a javascript on the load of a form that calls the FixFlicker function:
FixFlicker = function(){ var head = window.parent.window.document.getElementsByTagName('head')[0]; var link = window.parent.window.document.createElement('link'); link.rel = 'stylesheet'; link.type = 'text/css'; link.href = '/WebResources/theNameOfMyStyleSheet'; link.media = 'all'; head.appendChild(link); }
This should solve your problem