Did a quick search and couldn't find this decision on the forums. The case is R. v. Capobianco, a somewhat recent Court of Appeal decision.
The Courts have ruled that for the offence of failing to drive in a marked lane, the Crown must show:
1) The accused failed to drive in the marked lane AND
2) The manoeuvre was not made in safety
It used to be sufficient to simply show that you weren't driving in the marked lane. The requirement to show the action was unsafe adds a further burden to the Crown.
Case law link: http://www.canlii.org/en/on/onca/doc/20 ... ca589.html