Say you were to add a methyl cuprate to acrolein (this example is made-up but the general idea stands). The reaction is given in the scheme below:
$$\ce{H2C=CH-CH=O + MeCuMgBr -> Me-CH2-CH=CH-OCuMgBr}\tag{1}$$
The initial intermediate is not the ketone but the 4-substituted but-1-en-1-olate. The metal has been added to position 1, the organic residue to position 4. Hence 1,4-addition.
Only after aquaeous workup will the but-1-en-1-ol be formed which can tautomerise to give the aldehyde.
You may think of this as a 1,4-addition followed by 1,3-hydrogen rearrangement. Or as a 1,4-addition followed by C-protonation of the resulting enolate.