Not sure what might be going on there... What Fireworks version and what operating system are you using?
Also, does the same problem occur using a simple rectangle with a gradient fill?
Now that I think of it, some users have reported problems with panels not responding to changes on the canvas. If possible, try closing all applications, shutting down and restarting your computer, and then starting Fireworks... Now see if the problem has cleared up.
Using CS6, thinking about it I think one of the presenters @ presentation recently had a similar problem... I'll try your suggestions and keep more details over the next few weeks.
another weird experience... Created tiff (.tif) in FW (default?) and then copied buttons into DW but the button set would not display. Saved images as .jpg, modified CSS to look for .jpg iso .tif and bingo, works fine??
The .tif file format isn't generally recommended for web use; it's intended more for print. Historically, some browsers haven't supported the format, if I recall correctly, though many of them may do so now. (Just checked Firefox and Safari, and both seem to display the format just fine.)
It could be that Dreamweaver doesn't recognize the .tif format. (I'm a little lazy to test this theory at the moment, but it seems quite likely.) Here's one rather old thread on this topic: http://forums.adobe.com/thread/26977
Incidentally, this is straying from the topic of your original post and would have been better posted as a new discussion.
I had a problem recently with the css panel (Fireworks 188.8.131.52, Mac Lion). Created a rounded rectangle, with a gradient and drop shadow. The CSS panel ignores the drop shadow.