In my ubuntu/linux environment, I has a roundup instance whose directory is :
/home/broader/roundup/data
and a hyperdb.FileClass instance whose name is 'crecord' is located as below:
/home/broader/roundup/data/db/files/crecord
When call the hyperdb.exportFilename() method,it returns a incorrect file
path as below:
/home/broader/roundup/data/db/crecord-files/0/crecordx
but the right path should be :
/home/broader/roundup/data/db/files/crecord/0/crecordx

So, I think its maybe a bug,because in roundup all the hyperdb.FileClass instances will be saved to ../files/(classname)/(0...)/classname(0~...) , not ../classname-files/(0...)/classname(0~...) 
By the way, I have tested it on Windows environment(XP/python2.5.2/roundup1.4.5.1) also, and got the same result as on Linux/Ubuntu.

Best Regards!