In bug #646882 it turned out that whereis utility ignores my $PATH and reports places where a binary is present. If an application relies on the listing of full paths to whichever binary, it may on Gentooo PREFIX-ed installations execute an executable from say /usr/bin/foo instead of ${EPREFIX}/usr/bin/foo . That could be a different arch and may not even work.
(In reply to Martin Mokrejš from comment #0) > If an application relies on the listing of full paths to whichever binary[...] ...it definitely shouldn't rely on whereis to provide it. FTFY.
I am not sure if this a bug. Please file a bug with upstream at https://github.com/karelzak/util-linux/issues