java8 app does not refresh

[teledyn]

Ubuntu 17.10 on both client and server, server is running xfce4, client is gnomeshell

using vncviewer (TigerVNC) from current apt repo, if I click on an item in a java8 app, the app often does nothing until I minimize it, for example, clicking a button, the button highlights to indicate the click, but the action behind the button does not trigger until the app loses focus, it then starts processing which will update the display on restoring the view.

using nxclient / nxserver, the same client and server setup (except with nx) works fine, actions cause reliable and immediate response in the java8 app.

Let me know if there are any further logs/tests I can do to help