I think you are using the wrong function for your purpose! You're asking for the tablename which is stored in a QVD file. The tablename is the name of the original tablename from your datamodel, not the name of the file you saved your table to.
If you open your QVD in a text editor then you see the original tablename in the metadata :
What is the name of the table when you look in your QVD? With or without underscores?
I'm using QV12.