<dll-path>'$ORIGIN' is prefixed by path with gcc

Jamroot.jam:
build-project p ;

p/Jamfile.jam:
lib a : a.cpp : <link>shared ;
exe p : p.cpp : <library>a ;
install install : p : <install-dependencies>on <dll-path>'$ORIGIN' ;

./b2
...found 20 targets...
...updating 8 targets...
gcc.compile.c++ p/bin/gcc-4.9.4/debug/a.o
gcc.link.dll p/bin/gcc-4.9.4/debug/liba.so
gcc.compile.c++ p/bin/gcc-4.9.4/debug/p.o
gcc.link p/bin/gcc-4.9.4/debug/p
common.copy p/install/a.cpp
gcc.link.dll p/install/liba.so
common.copy p/install/p.cpp
gcc.link p/install/p
...updated 8 targets...

objdump -x -a p/install/p | grep RPATH
   RPATH                p/$ORIGIN

I expected dll-path to be set unmodified. Is this intended, and if so, how do I prevent it? I haven't pinpointed exactly when this changed, 
but it worked a couple years ago. This is using master at c3dc95d3ac0219a0f774e6d382ed91d290cbde80.

Thanks,
-Matt

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