In Bangalore, this is a common practice that a land owner and builder will get together based on a Joint Development Agreement (JDA) and then sell flats. If you are buying an apartment in such a project then there will be two separate agreements that you will have to sign with the builder, Sale and Construction. However, if the builder owns the land and is constructing the apartment as well then there will only be a single Sale Agreement. Both scenarios are quite prevalent in Bangalore and therefore do not warrant any cause of concern.
Hope this helps.