Suppose I have a wavefunction which collapses to a certain eigenstate after a measurement of energy. In that state, I perform a calculation of position and obtain a certain position value, say $x_0$. After some time, if I perform a calculation of position again, will I obtain $x_0$ again, or will it be something different?
What I have learnt is that, if on performing a calculation of energy, the wavefunction collapses, then a calculation on the collapsed wavefunction will give the same energy, at any time later and for any observer. Does the same hold true for any observable?