Traffic stop doesn't have much to do with it. It's the presence of the LTCH that should stop all further inquiries/actions regarding the firearm. I do believe that the standard holds whether one is stopped in his vehicle or on the street.
Found it: Washington v State, 2010. Presentation of LTCH immediately limits grounds for fishing expedition by LE (regarding the firearm), as well as the bounds of "officer safety" claims used to justify said firearm's seizure.
That standard doesn't apply. Washington was removed from his vehicle, and cuffed, meaning he had no access to the firearm (which was under his seat). It's obvious that officer safety doesn't apply, and the seizure of the weapon out of bounds. It's quite another thing, in the eyes of the court, when an officer seizes a firearm on the person of a stopped motorist.