Filters work fine on files in a directory on my hard drive. For example with Filter=Hello, Dopus only shows files with a name containing "Hello".
However, nothing is filtered out on in a Lister showing the files in DVD directory. Is there some setting that disables filters on DVD drives or is this a bug?
If it's a writeable DVD, and you have the option switched on to support the Windows CD burning system, then the display of the CD is provided by Explorer (and Opus only hosts it) which means Opus filters, etc don't have any effect.
Sorry, it was actually a CD-R (not DVD). In any case, I turned off Windows CD burning system (using gpedit.msc) and rebooted. Filters still don't work 
p.s. Win7 64-bit
Try turning off the Windows CD burning option in the Opus Preferences as well.
That did the trick. Thanks.
p.s. I wonder if it was even necessary to turn it off in Windows?
No, not necessary.