The "effect" is quite real, but I don't believe there's a name for it. It has to do with rotational stability and the intermediate axis theorem.
I'm sure you've also observed this effect when throwing a spatula, frying pan, or remote control.
In terms of rotational inertia, the "easiest" axis of rotation for the racquet is straight through the handle. The "hardest" axis of rotation would be straight down (perpendicular to the strings).
But when there's rotation along the "intermediate" axis (the one you describe), the other axes (especially the "easiest") become extremely sensitive to random perturbations.
If you could flip or spin the racquet so that it turned exclusively
about one of its three principal axes, it would continue to spin about
that axis indefinitely. That's why they're called principal axes. But
in a real flip there is always some mixture of motions about all three
axes. Here is where the intermediate axis theorem enters the picture:
while a racquet spinning mostly about either the
low-rotational-inertia axis or high-rotational-inertia axis will be
relatively unaffected by extraneous motion about the other two axes, a
racquet that is spinning mostly about the
intermediate-rotational-inertia axis is exquisitely sensitive to any
accidental motion about those other two axes. Even a tiny amount of
unintended motion about those axes will cause the racquet to wobble