Running demo-x11.jar and clicking one of X11 dependent buttons or using new X11.XEvent() somewhere in code causes this:

Exception in thread "AWT-EventQueue-0" java.lang.Error: Structure.getFieldOrder() on class com.sun.jna.platform.unix.X11$XDestroyWindowEvent does not provide enough names ([display, send_event, serial, type, window]) to match declared fields ([display, event, send_event, serial, type, window])
at com.sun.jna.Structure.getFields(Structure.java:860)
at com.sun.jna.Structure.deriveLayout(Structure.java:983)
at com.sun.jna.Structure.calculateSize(Structure.java:908)
at com.sun.jna.Structure.allocateMemory(Structure.java:345)
at com.sun.jna.Structure.ensureAllocated(Structure.java:321)
at com.sun.jna.Structure.ensureAllocated(Structure.java:311)
at com.sun.jna.Structure.size(Structure.java:374)
at com.sun.jna.Native.getNativeSize(Native.java:985)
at com.sun.jna.Structure.getNativeSize(Structure.java:1769)
at com.sun.jna.Structure.getNativeSize(Structure.java:1762)
at com.sun.jna.Structure.validateField(Structure.java:958)
at com.sun.jna.Structure.validateFields(Structure.java:972)
at com.sun.jna.Structure.(Structure.java:186)
at com.sun.jna.Structure.(Structure.java:180)
at com.sun.jna.Structure.(Structure.java:167)
at com.sun.jna.Structure.(Structure.java:159)
at com.sun.jna.Union.(Union.java:37)
at com.sun.jna.platform.unix.X11$XEvent.(X11.java:1334)
at jnacontrib.x11.api.X$Window.clientMsg(X.java:1061)
at jnacontrib.x11.api.X$Window.clientMsg(X.java:1033)
at jnacontrib.x11.api.X$Window.activate(X.java:687)
at jnacontrib.x11.demos.XDesktopDemo$3.actionPerformed(XDesktopDemo.java:95)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3312)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

Issue exists both in latest master and JNA 3.5.1. Test machine was Ubuntu 12.10, amd64