I've done a similar thing to you but using a Panasonic disc recorder, rather than a VCR. Mine worked perfectly, so I was able to copy stuff from TiVo to disc in order to create space on the TiVo. I would suggest that you check the SCART connections, as a bad connection could give the results you're getting.
I'm confused about whether your problem arises when you are making the copy or when you play back the tape you have made.
To make the copy you must set the input of the Sanyo to be the SCART connected to the TiVo and set the input of the TV to be the Sanyo. At that point the TV should be displaying what the TiVo is transmitting (check by eg, viewing your recordings list on the TiVo). Start the Sanyo recording and then set the TiVo playing the program you want to copy. You should end up with the Sanyo copying your TiVo program and the TV picture and sound showing the recording.