Open attached document, place cursor at the beginning of numbered paragraph. Now
press Backspace key four times to 
- delete label
- turn off numbering
- delete first line indent
- delete indent before paragraph
as described in spec "NumberingBullets1" chapter 7.4

The current behaviour is wrong; in the first step The label and the first line
indent will be deleted, second tries to turn off numbering (as the Undo button
states, but only the number position values seem to be removed, the num-context
keeps alive)
The paragraph indent will not be removedin last step - the paragraph break will
be removed.