Um, yeah? I would say most LEO's do know the law as it tends to bite them in the tail end if they would do an enforcement action and be wrong. If Idmaster were to enforce his interpretation of the law (mind you, my post also discussed this point ad nauseum) and it was to be found in court to be wrong, depending upon which agency he worked, the citation would be dismissed, a letter would be sent by the D.A. to his agency (dependent upon the D.A.'s office and their relationship with his agency) and he would be open to a complaint by the citizen and possible civil remedies from a lawsuit. An officer wouldn't be covered under governmental immunity if he was plain wrong and couldn't be covered under good faith.
That's one reason why the attorney general's office and most local D.A.'s offices conduct training with law enforcement on the new statutes, changes in statute and new non-funded mandates required by statute in order to keep the majority of law enforcement out of trouble. Most good agencies will enhance that training with training of their own on a monthly basis, discussing new case law, new trends, new tactics, new municipal ordinances, etc. Continuous training is necessary in law enforcement to keep up with all the ever changing statutes, case law, circumstances, and such.