It would be handy if there were a way to select enum parameters in the SOAP field that were marked with the [Flags] attribute in the UI. Today your presented with a free form textbox and must type in the enum values which can be error prone and tedious when dealing with bitmask enums. Perhaps some sort of popup with checkbox? Normal enums give you a convenient dropdown list, even that would be helpful.
Case #00113986: enums marked with Flags attribute don't bubble up into the UI
I also saw an similar request on the forums...
http://community.smartbear.com/t5/SoapUI-Open-Source/SoapUI-and-Flags/m-p/42613/highlight/true#M16627