Bug report

As described in #11663 (review):

Something funny is going on here (I know it was already there before, but still seems worth pointing out): we take x and y of any shapes and flatten them (they just need to have the same size), but c has to match either the shape of x or y, not just the size.

In other words the following "work" (i.e. perform an implicit ravel()):

scatter(np.arange(12).reshape((3, 4)), np.arange(12).reshape((4, 3)), c=np.arange(12).reshape((3, 4)))
scatter(np.arange(12).reshape((3, 4)), np.arange(12).reshape((4, 3)), c=np.arange(12).reshape((4, 3)))

but the following fail:

scatter(np.arange(12).reshape((3, 4)), np.arange(12).reshape((4, 3)), c=np.arange(12).reshape((6, 2)))
# and even
scatter(np.arange(12).reshape((3, 4)), np.arange(12).reshape((4, 3)), c=np.arange(12))

Of course that last one has the best error message (irony intended):

ValueError: 'c' argument has 12 elements, which is not acceptable for use with 'x' with size 12, 'y' with size 12.