Silk Touch on a pick no longer works on glass

When using a silk touch pick on a placed glass block, the breaking animation plays but the block doesn't break (the block doesn't drop as an item either). The block itself remains where it was previously – either it pops back into the clients' view, or if it appears to no longer be there, trying to place another block in the same place makes the original glass block re-appear.

Silk touch shovels still appear to break the blocks successfully (& drop the glass block as an item).

Is silk touch on a pick still supposed to allow breaking/collection of glass blocks?