Assertion failed: (props->direction != HB_DIRECTION_INVALID)

[springmeyer]

running this test code with latest harfbuzz from github (v0.9.16) on OS X I get:

$ ./harfbuzz-test
Assertion failed: (props->direction != HB_DIRECTION_INVALID), function hb_shape_plan_create, file hb-shape-plan.cc, line 93.
Abort trap: 6

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib          0x00007fff86bb7d46 __kill + 10
1   libsystem_c.dylib               0x00007fff92398df0 abort + 177
2   libsystem_c.dylib               0x00007fff92399e2a __assert_rtn + 146
3   libharfbuzz.0.dylib             0x00000001004b0877 hb_shape_plan_create + 2135
4   libharfbuzz.0.dylib             0x00000001004b1269 hb_shape_plan_create_cached + 1065 (hb-shape-plan.cc:289)
5   libharfbuzz.0.dylib             0x00000001004afeeb hb_shape_full + 75 (hb-shape.cc:259)
6   harfbuzz-test                   0x0000000100005bf6 mapnik::text_shaping::process_text(icu_49::UnicodeString const&) + 164
7   harfbuzz-test                   0x0000000100005df0 mapnik::text_layout::shape_text() + 110
8   harfbuzz-test                   0x00000001000048eb main + 811
9   harfbuzz-test                   0x0000000100004594 start + 52