  Recently Pasetto et al. have proposed a new method to derive a convection
theory appropriate for the implementation in stellar evolution codes. Their
approach is based on the simple physical picture of spherical bubbles moving
within a potential flow in dynamically unstable regions, and a detailed
computation of the bubble dynamics. Based on this approach the authors derive a
new theory of convection which is claimed to be parameter free, non-local and
time-dependent. This is a very strong claim, as such a theory is the holy grail
of stellar physics.
  Unfortunately we have identified several distinct problems in the derivation
which ultimately render their theory inapplicable to any physical regime. In
addition we show that the framework of spherical bubbles in potential flows is
unable to capture the essence of stellar convection, even when equations are
derived correctly.
