Boy its a mystery to me. I'll be watching to see who figures this one out.
I have used the same LV blade/cap iron in a Stanley #4 with no problems.
I notice you've got the frog set right to the edge of the mouth and it can be moved back a little.
Have you tried that?
The only thing that comes to my mind is to confirm that is the correct frog for that plane.
Short of that, grinding the blade shorter is the only thing I can think of and I know you don't want to do that!