Could I say that the “Locking” in Blender 2.76 takes a “Sample” of the “Topology” under the “Brush” at the beginning of the “Stroke” and used these “Parameters” for the whole “Stroke” instead of continuously resampling the “Topology” for each “Brush (Movement) Step” ?
There seems to be a “Locking” as the “Quick Tip” for “Use Original Normal” suggests:

But the “When locked …” of that “Quick Tip” also suggests in my opinion that the “Locking” has to be set elsewhere.