dpkg-source: binary file contents changed

[Rafael Caetano dos Santos <rcaetano@linux.ime.usp.br>]

While trying to build a package (using debhelper), I got the following
message from dpkg-buildpackage:

dpkg-source: cannot represent change to foo: binary file contents changed

for every binary file foo (executable or library). 

What does it mean?
Should I do a 'make clean' after 'make install' in rules??

bye 
    Rafael Caetano <rcaetano@linux.ime.usp.br>