If you are working on very large sized drawings, its common to have fonts of 200pt and higher.
The problem is, when fonts are 200-300 pts and above, the text wrapping seems to be broken, i.e. it wraps text, way before the edge of the boxshape...
(I've only tried this in Visio 2010)
The problem isn't the fonts. It's a very long standing bug in Visio that causes text wrapping on large scale drawings. I can't find a reference to it at the moment ...