JSpinner may have a text editor inside. The preferred size of JSPinner depends from this editor, which also depends from the font. Look like a have a bug when we calculate the size of the JSPinner using default font of editor and only after that we change the font of the editor to the font of spinner.
To reproduce this bug run this test:
http://cr.openjdk.java.net/~serb/8201552/webrev.01/test/jdk/javax/swing/GraphicsConfigNotifier/StalePreferredSize.java.html

See this line;
//TODO () -> new JSpinner(new SpinnerListModel(new String[]{HTML})),