ANSWER:

What these so called scholars say is wrong. 

The sunnah is to pray 4 rakah prayers into 2 rakah when traveling.

If a person refuses to shorten such prayers, he is going against the sunnah but his prayers are valid.

QUESTION: If m a traveller is it Sunnah or wajib to offer 2 rakat in zuhr, asar, Esha Salah ? Scholar say if a traveller offer 4 rakat in these 3 Salah, the Salah is invalid bcz shortening(praying 2 rakat instead of 4) is wajib for a traveller.