Description of problem:
Unselecting all plugins results in having all plugins selected

Version-Release number of selected component (if applicable):
0.7.1

How reproducible:
every time

Steps to Reproduce:
1.open plugin selection dialog
2.disable/unselect all plugins by clicking on selection-boxes (going from top to
bottom or bottom to top makes no difference)
3.close dialog
4.reopen dialog -> all plugins are selected again!
  
Actual results:
unselected plugins are selected again

Expected results:
unselected plugins should stay unselected, even when ALL are unselected

Additional info:
I have the 3 standard plugins 'local-track', 'md5sum' and 'md5sum-file' installed.
Described bug only happens if ALL plugins are unselected. Only unselecting 1 or
2 of the 3 plugins works ok.