wc -L reports a line-length of 8 for a tab-char. bug or feature?

I find no bug report related to this, and the following lines in the source file wc.c

    case '\t':
        linepos += 8 - (linepos % 8);

seem to deliberately choose to behave in this way, probably to give an hint for width needed to display the file on screen.

A quick alternative could be

echo -n $'\t' | tr '\t' ' ' | wc -L