"du" inconsistent block size

Question

I am getting inconsistent block sizes from du output

$ du -b acinclude.m4 aclocal.m4
2019    acinclude.m4
40203   aclocal.m4

$ du acinclude.m4 aclocal.m4
4       acinclude.m4  #  2019 /  512
40      aclocal.m4    # 40203 / 1024

What is causing this?

Answer 1

$ du --apparent-size acinclude.m4 aclocal.m4
2       acinclude.m4
40      aclocal.m4