Short 2nd \ Subject to 1st mortgage

When the second mortgage holder reviews a purchase sales contract where the second is being shorted and the contract specifies the first mortgage will be taken “subject to”, does this create any sort of problem for the second holder? Second question - do you point out to the seller tax implications when a mortgage is shorted (1099)? I have a disclosure that the seller signs which states that they will be liable for taxes on the discount, however do most of you verbally indicate this to the seller? Any and all input is appreciated - Mark.