Xpra: Ticket #729: do_paint_rgb24: no array-type handler for type buffer

I've hit this twice now, no idea how:

2014-11-06 15:23:36,956 do_paint_rgb24 error
Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/xpra/client/window_backing_base.py", line 282, in do_paint_rgb24
    success = (self._backing is not None) and self._do_paint_rgb24(img_data, x, y, width, height, rowstride, options)
  File "/usr/lib64/python2.7/site-packages/xpra/client/gl/gl_window_backing.py", line 453, in _do_paint_rgb24
    return self._do_paint_rgb(24, img_data, x, y, width, height, rowstride, options)
  File "/usr/lib64/python2.7/site-packages/xpra/client/gl/gl_window_backing.py", line 502, in _do_paint_rgb
    glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, self.texture_pixel_format, width, height, 0, pformat, GL_UNSIGNED_BYTE, img_data)
  File "latebind.pyx", line 32, in OpenGL_accelerate.latebind.LateBind.__call__ (src/latebind.c:989)
  File "wrapper.pyx", line 299, in OpenGL_accelerate.wrapper.Wrapper.__call__ (src/wrapper.c:6294)
  File "wrapper.pyx", line 161, in OpenGL_accelerate.wrapper.PyArgCalculator.c_call (src/wrapper.c:4241)
  File "wrapper.pyx", line 128, in OpenGL_accelerate.wrapper.PyArgCalculatorElement.c_call (src/wrapper.c:3601)
  File "wrapper.pyx", line 122, in OpenGL_accelerate.wrapper.PyArgCalculatorElement.c_call (src/wrapper.c:3520)
  File "/usr/lib/python2.7/site-packages/OpenGL/GL/images.py", line 457, in __call__
    return arrayType.asArray( arg )
  File "arraydatatype.pyx", line 174, in OpenGL_accelerate.arraydatatype.ArrayDatatype.asArray (src/arraydatatype.c:4221)
  File "arraydatatype.pyx", line 57, in OpenGL_accelerate.arraydatatype.HandlerRegistry.c_lookup (src/arraydatatype.c:2230)
TypeError: ("No array-type handler for type <type 'buffer'> (value: <read-write buffer ptr 0x7fdd9c142cc0, size 630736) registered", <OpenGL.GL.images.ImageInputConverter object at 0x436dbd0>)