The silk touch enchantment book when you mine a 'silk touch affected block' would give you the actul block rather then it's by-product.

The silk touch enchantment book would act like a tool enchanted with silk touch for example: Mining a grass block would give you the grass block itself rather then a dirt block.

A Minecraft YouTuber 'AntVenom' has made more detail about this in one of the parts of he video where he explains the bug.

Video: https://www.youtube.com/watch?v=BrSRXcWPB3Y