I took VB from Agra to RKMP on March 21 (wanted Shatabdi but it was wait listed in executive class). The VB was late by 3 hours and had to run behind Mumbai Rajdhani all the way. So, 6 hour journey turned to 9 hours and the problem was technical.
It is possible that VB rake limits the option to an alternative loco unlike regular LHB rake. I was also VERY disappointed with dirty lavatories in both, E1 and E2. I would have assumed it to be clean at its first stop...
more... (and relatively empty train) but apparently, it was never cleaned at its starting point either. Later, my cousin in Bhopal told me that they do not take VB for that reason... it is not maintained as well as Shatabdi.