Blocking/jumping of images in slideshow

when click in the bottom area of the window when in slideshow it stops during fading, blocks a while and then jumps fast some images ahead.

there is this log:

 C:\elisa_win32\upicek\elisa-plugins\elisa\plugins\poblesec\player_slideshow.py in on_selected_item_changed(background=<ListFading object at 0x362a670 (elisa+pl
ugins+pigment+widgets+list+List at 0x35f25e0)>, item=None, prev_item=None)
  168
  169 def on_selected_item_changed(background, item, prev_item):
  170 index = self.background.model.index(item)
  171 self._set_current_index(index)
  172
index undefined
self = <Slideshow object at 0x362a620 (elisa+plugins+poblesec+player_slideshow+Slideshow at 0x35f25d0)>
self.background = <ListFading object at 0x362a670 (elisa+plugins+pigment+widgets+list+List at 0x35f25e0)>
self.background.model = []
self.background.model.index = <built-in method index of List object at 0x035A65D0>
item = None
<type 'exceptions.ValueError'>: list.index(x): x not in list
    __class__ = <type 'exceptions.ValueError'>
    __delattr__ = <method-wrapper '__delattr__' of exceptions.ValueError object at 0x03F015D0>
    __dict__ = {}
    __doc__ = 'Inappropriate argument value (of correct type).'
    __getattribute__ = <method-wrapper '__getattribute__' of exceptions.ValueError object at 0x03F015D0>
    __getitem__ = <method-wrapper '__getitem__' of exceptions.ValueError object at 0x03F015D0>
    __getslice__ = <method-wrapper '__getslice__' of exceptions.ValueError object at 0x03F015D0>
    __hash__ = <method-wrapper '__hash__' of exceptions.ValueError object at 0x03F015D0>
    __init__ = <method-wrapper '__init__' of exceptions.ValueError object at 0x03F015D0>
    __new__ = <built-in method __new__ of type object at 0x10232E10>
    __reduce__ = <built-in method __reduce__ of exceptions.ValueError object at 0x03F015D0>
    __reduce_ex__ = <built-in method __reduce_ex__ of exceptions.ValueError object at 0x03F015D0>
    __repr__ = <method-wrapper '__repr__' of exceptions.ValueError object at 0x03F015D0>
    __setattr__ = <method-wrapper '__setattr__' of exceptions.ValueError object at 0x03F015D0>
    __setstate__ = <built-in method __setstate__ of exceptions.ValueError object at 0x03F015D0>
    __str__ = <method-wrapper '__str__' of exceptions.ValueError object at 0x03F015D0>
    args = ('list.index(x): x not in list',)
    message = 'list.index(x): x not in list'

The above is a description of an error in a Python program. Here is
the original traceback:

Traceback (most recent call last):
  File "C:\elisa_win32\upicek\elisa-plugins\elisa\plugins\poblesec\player_slideshow.py", line 170, in on_selected_item_changed
    index = self.background.model.index(item)
ValueError: list.index(x): x not in list