- in a projection view select e.g. the front view
- go to the View tab and there to the Lines section
result: the default line width is "0.7"
- now use the arrow button of the field to decrease the width
result: you end up with "-0.3"
So there are 2 bugs (applies for all widths):
- the width has no unit (I guess it is pt)
- the width can be negative