I think this may be a different problem, but I discovered that moving the mouse about a lot while selecting text (I think it helps if the page is shorter than the viewport) can get: ==14918== Conditional jump or move depends on uninitialised value(s) ==14918== at 0x80F6F65: fl_utf8fwd (fl_utf.c:228) ==14918== by 0x8090434: dw::fltk::FltkPlatform::nextGlyph(char const*, int) (fltkplatform.cc:558) ==14918== by 0x808F671: dw::Textblock::sendSelectionEvent(dw::core::SelectionState::EventType, dw::core::MousePositionEvent*) (layout.hh:302) ==14918== by 0x808F849: dw::Textblock::motionNotifyImpl(dw::core::EventMotion*) (textblock.cc:539) ==14918== by 0x809EDA2: dw::core::Layout::motionNotify(dw::core::View*, int, int, dw::core::ButtonState) (layout.cc:795) ==14918== by 0x8097BB3: dw::fltk::FltkViewBase::handle(int) (fltkviewbase.cc:272) ==14918== by 0x80A8AFE: send(int, Fl_Widget*, Fl_Window*) (Fl.cxx:1035) ==14918== by 0x80A92A5: Fl::handle_(int, Fl_Window*) (Fl.cxx:1347) ==14918== by 0x80A8B6B: Fl::handle(int, Fl_Window*) (Fl.cxx:1115) ==14918== by 0x80DBD1C: do_queued_events() (Fl_x.cxx:198) ==14918== by 0x80DC15B: fd_callback(int, void*) (Fl_x.cxx:340) ==14918== by 0x80DBFF1: fl_wait(double) (Fl_x.cxx:257)