Cannot choose mask or watermark image

This happens under Ubuntu MATE 15.04

When clicking on "Mask" or "Mark" in the GUI, it writes "loading..." and no popup window appears.

If phatch was stated from terminal window, the following is printed there:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_core.py", line 16763, in <lambda>
    lambda event: event.callable(*event.args, **event.kw) )
  File "/usr/share/phatch/phatch/lib/pyWx/popup.py", line 364, in OnChange
    icon_size=self.icon_size,
  File "/usr/share/phatch/phatch/lib/pyWx/imageFileBrowser.py", line 102, in __init__
    self.image_list = ListCtrl(self.panel, files, icon_size)
  File "/usr/share/phatch/phatch/lib/pyWx/imageFileBrowser.py", line 54, in __init__
    pil_wxBitmap(open_thumb(file, size=icon_size)))
  File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_gdi.py", line 6735, in Add
    return _gdi_.ImageList_Add(*args, **kwargs)
wx._core.PyAssertionError: C++ assertion "(bitmap.GetWidth() >= m_width && bitmap.GetHeight() == m_height) || (m_width == 0 && m_height == 0)" failed at ../src/generic/imaglist.cpp(66) in Add(): invalid bitmap size in wxImageList: this might work on this platform but definitely won't under Windows.