single (debug) binaries from base source tree install fails (/usr/bin/true)

Hello,

I try to install a DEBUG_FLAGS=-g version of top since it core dumps on 
my 8.0-RELEASE box.
Compiling works with warnings, but installing fails with superfluous 
"/usr/bin/true" after install:

install /usr/bin/true -o root -g wheel -m 555   top /usr/bin
install: -o: No such file or director

Can someone please tell me how to correctly replace single binaries in 
the base system with debug versions?

Thanks,

-Harry