Random Blank Dialog boxes

My SoapUI occasionally shows random blank dialog boxes, none by request. This morning it has blank dialogs titled "Generate TestSuite" (2 of those), "UpdateDefinition", "New SOAP Project", "Add WSDL", and "Progress". Fortunately they are not modal, but they won't go away without restarting the app. Any ideas? 

[I have the non-pro version 5.4.0 "Build Date: 20171204-0633"]