If a user does something like

fig, axs = plt.subplots(2, 2, layout='constrained')
..
plt.tight_layout()

tight_layout is called, and constrained_layout is ignored. This was originally done because constrained_layout was experimental. However, people seem to think constrained_layout is not working because they have copy-and-pasted, or reflexively added plt.tight_layout.

I'd propose that we at least warn if plt.tight_layout is called on a figure with an active layout manager. I'd also be open to this being an error.