I have plasmid which amplified by primers in PCR and its  giving to band So cut the upper band, gel purified it and after Nanodrop run the gel again now it is giving the single band.

I used this for cloning, I have got colonies, I picked colony and screen it by isolating plasmid then i rechecked it vector at that same primer and same PCR conditions now it is giving two band again.

Now tell me when i used single band product in cloning why it is giving two band again for vector rechecking ?