Hang with CubicBezierSmooth powerstroke interpolator

(Trisquel 7.0, trunk r14461) Open the attached file, then apply the powerstroke LPE to it. The default interpolator applied is CubicBezierFit, which does not hang the program, although the following warnings are printed to STDERR:

** (inkscape:5814): WARNING **: Exception during LPE Power stroke execution.
 lib2geom exception: Invariants violation (./2geom/piecewise.h:155)

** (inkscape:5814): WARNING **: Exception during LPE Power stroke execution.
 lib2geom exception: Invariants violation (./2geom/piecewise.h:155)

Now change the interpolator to CubicBezierSmooth; Inkscape now hangs. Backtrace after SIGINT:
#0 0x00007ffff00c4f24 in _int_free (av=0x7ffff0404760 <main_arena>, p=0x84509c0, have_lock=0) at malloc.c:3814
#1 0x0000000000c8906a in deallocate (this=<optimised out>, __p=<optimised out>) at /usr/include/c++/4.8/ext/new_allocator.h:110
#2 _M_deallocate (this=<optimised out>, __n=<optimised out>, __p=<optimised out>) at /usr/include/c++/4.8/bits/stl_vector.h:174
#3 ~_Vector_base (this=0x7fffffffb5c0, __in_chrg=<optimised out>) at /usr/include/c++/4.8/bits/stl_vector.h:160
#4 ~vector (this=0x7fffffffb5c0, __in_chrg=<optimised out>) at /usr/include/c++/4.8/bits/stl_vector.h:416
#5 ~SBasis (this=0x7fffffffb5c0, __in_chrg=<optimised out>) at ./2geom/sbasis.h:69
#6 RescaleForNonVanishingEnds (MM=..., ZERO=0.0001) at 2geom/sbasis-geometric.cpp:110
#7 0x0000000000c8a668 in Geom::unitVector (V_in=..., tol=tol@entry=0.01, order=order@entry=3) at 2geom/sbasis-geometric.cpp:229
#8 0x00000000007b5bd5 in Geom::touching_circle (curve=..., tol=0.01, t=0) at live_effects/lpe-powerstroke.cpp:114
#9 0x00000000007b644e in Inkscape::LivePathEffect::path_from_piecewise_fix_cusps (B=..., y=..., jointype=jointype@entry=Inkscape::LivePathEffect::LINEJOIN_EXTRP_MITER_ARC, miter_limit=4, tol=0.01)
    at live_effects/lpe-powerstroke.cpp:424
#10 0x00000000007b8cbf in Inkscape::LivePathEffect::LPEPowerStroke::doEffect_path (this=0x84e6400, path_in=...) at live_effects/lpe-powerstroke.cpp:640
#11 0x000000000073e8cb in Inkscape::LivePathEffect::Effect::doEffect (this=0x84e6400, curve=0x84dfce0) at live_effects/effect.cpp:524
#12 0x00000000005844ca in SPLPEItem::performPathEffect (this=this@entry=0x8118fe0, curve=curve@entry=0x84dfce0) at sp-lpe-item.cpp:254
#13 0x00000000005a2d90 in SPPath::update_patheffect (this=0x8118fe0, write=<optimised out>) at sp-path.cpp:340
#14 0x0000000000584859 in sp_lpe_item_update_patheffect (lpeitem=<optimised out>, wholetree=<optimised out>, write=<optimised out>) at sp-lpe-item.cpp:325
#15 0x000000000059ec94 in emit (_A_a2=@0x7fffffffc98c: 1, _A_a1=@0x7fffffffc998: 0x80c6b40, impl=0x838fd20) at /usr/include/sigc++-2.0/sigc++/signal.h:1252
#16 emit (this=0x80c6be8, _A_a2=@0x7fffffffc98c: 1, _A_a1=@0x7fffffffc998: 0x80c6b40) at /usr/include/sigc++-2.0/sigc++/signal.h:2891
#17 SPObject::emitModified (this=this@entry=0x80c6b40, flags=flags@entry=0) at sp-object.cpp:1236
#18 0x0000000000550528 in SPDefs::modified (this=<optimised out>, flags=0) at sp-defs.cpp:68
#19 0x000000000059ebf0 in SPObject::emitModified (this=this@entry=0x8177400, flags=flags@entry=0) at sp-object.cpp:1234
#20 0x0000000000577f61 in SPGroup::modified (this=this@entry=0x7bc0a30, flags=0, flags@entry=2) at sp-item-group.cpp:213
#21 0x00000000005ab740 in SPRoot::modified (this=0x7bc0a30, flags=2) at sp-root.cpp:301
#22 0x000000000059ebf0 in SPObject::emitModified (this=0x7bc0a30, flags=flags@entry=0) at sp-object.cpp:1234
#23 0x00000000004abbba in SPDocument::_emitModified (this=this@entry=0x1e5e4e0) at document.cpp:1003
#24 0x00000000004ac36a in SPDocument::_updateDocument (this=this@entry=0x1e5e4e0) at document.cpp:1170
#25 0x00000000004ac4a7 in SPDocument::ensureUpToDate (this=this@entry=0x1e5e4e0) at document.cpp:1193
#26 0x00000000004b9f1d in Inkscape::DocumentUndo::maybeDone (doc=doc@entry=0x1e5e4e0, key=key@entry=0x0, event_type=239, event_description=...) at document-undo.cpp:153
#27 0x00000000004ba40c in Inkscape::DocumentUndo::done (doc=doc@entry=0x1e5e4e0, event_type=<optimised out>, event_description=...) at document-undo.cpp:99