When the pots sit for a while, the ingredients settle and the heaviest particles move to the top and the lightest to the bottom.  This can sometimes mean that the flavour profile changes.   For example, we sometimes find that without mixing / shaking the bhuna pot, it can taste more of fenugreek than any other ingredient but after the mix, the flavour balance is restored.
Therefore, we suggest shaking the pot before each use!
Have a read of this article for a clearer explanation!