Yes, this is "fertilizer burn", basically the dry salts in the fertilizer have sucked the water out of the plant cells, it is a bit like putting salt on a slug.Looks like those melted ones had fertilizer granulars on their leaves.
No that's fine as fertiliser, I use what ever is "for sale" at the end of the summer. Have a look here: <"Off the shelf ferts..">.Ok, I was hoping they will grow better since I had some leftover fert for household plants.