If the font size of some text is equal to whatever you set the DefaultAttr font size to, the WPToolBar font size shows as blank when the text cursor is placed on that text.
For example, if you set some text to a font size of 12 when the DefaultAttr is set to 11, then placing the cursor on that text the toolbar font size works fine. Without changing anything else, set the DefaultAttr font size to 12, and reload the text. Now when you place the text on that size 12 text, the toolbar shows a font size of nothing.
WPTools 5.19 and earlier, D7, WinXP
Eric