Silk touch pics not silk touching on last use.

Silk touch pics not silk touching on last use.

What I expected to happen was that the pic would use the effect of silk touch on its last use.

I was mining some coal with my silk touch pic but it was its last use and when it broke mining the coal it dropped coal ore.

1. get a silk touch pic on its last use.
2. break a coal ore block.
3. coal ore will drop coal not coal ore