I was trying to lay out a dialog that used the Matisse layout manager and included some JLabels that used HTML tags to format the content. Although it looked fine in the NetBeans GUI designer, previewing the dialog showed that the content at the bottom of the dialog had disappeared because the dialog wasn't being made large enough. After a lot of fiddling around, it turns out that this is because Matisse can't determine the size of the JLabel properly if the text in it wraps over more than one line. The workaround is simple - insert
<br> tags at the points at which the text wraps onto a new line, then the size of the JLabels can be determined correctly.