Constraint popup closes Window

<?xml version="1.0" encoding="utf-8"?>
<window>
	<toolbarbutton label="Pop" onClick="win1.doPopup()" />

	<window visible="false" closable="true" id="win1" border="normal" width="600px" height="300px">
		<caption label="Test" />
		<label>Test</label>
		<textbox constraint="no empty" />
		<label>Click in textbox, then click in whitespace below to trigger constraint popup. Then click X on popup - window closes.</label>
	</window>	
</window>