UnsupportedFlavorException not thrown when getting unsupported data from system Clipboard

Attempting to retrieve an unsupported type of data from the System Clipboard returns null rather than throwing an UnsupportedFlavorException when the test is run on a single VM. The same test performs as expected across VM instances.

See attached test case.

Launch an instance of the test case (you can change the sample image URL if required).
Click the button labelled "Copy", and the console will show "Image copied to clipboard"
Click the button labelled "Paste", and the console will show "String pasted from clipboard : null"
This is incorrect behavior.

Launch a second instance of the same test case.
On the first window click the "Copy" button.
On the second window click the "Paste" button. The console shows "java.awt.datatransfer.UnsupportedFlavorException: Unicode String" as expected.