get src file by mmap, size is zero: Tape Backup "fails"

[iamfreaky]

Hello,

I recieved the following while doing a tape backup.
'get src file by mmap, size is zero'. After the error the tape get rewind and ejected.

I cant say that it happens everytime there is a file without any content, but in my case only changing the file and adding content to it, it became possible to do the backup.

Is this expected behaviour ? And if so can it be changed that empty files are getting written to tape ?