I think the 'quantum eraser' will interest you (wikipedia.org/wiki/Quantum_eraser_experiment#Introduction, see long answer below). It's weird that every light transmission/reflection/absorption event is probabilistic (Feynman's rules) and that a polarizer can 'label' a photon's polarization state on output (see below)...
"Although the nonlocality of quantum mechanics is most apparent in tests of Bell’s inequalities, it also plays a central
role in experiments exploring complementarity. One such, the “quantum eraser,” was discussed by Scully, Englert and
Walther  in connection with the micromaser.
...This particular version of the quantum eraser has a straightforward classical-wave explanation when the light source is describable in terms of coherent states. Thus it could be argued that there is nothing particularly quantum about this quantum eraser. Nevertheless, Jordan has proposed a similar Mach-Zehnder version of this experiment , in which he has argued on the basis of the correspondence principle that despite the existence of a classical explanation, such first-order interference experiments can be interpreted as true quantum erasers.
...We stress that it is the mere possibility
of obtaining which-path information that destroys the interference; no actual polarization measurements need to be
My understanding: They say that the first two polarizers are considered "labelers", since they determine polarized state output. And as stated, this 'which path test' quantum mechanically entangles the photons, which is evident as a wave-particle-duality when the 'test' involves interference.
Here's a cool description by Scientific American: arturekert .org/miscellaneous/quantum-eraser.pdf
"Wave-particle duality, which represents the complementary nature of the wavelike and particlelike behaviors of a quantum system, is perhaps the example that has garnered the greatest share of attention. The wavelike behavior is manifested in interference experiments. However, when a welcher-weg ~which-path! measurement is carried out on an interfering system, the system becomes entangled with the measuring apparatus, so that the paths of the system become distinguishable, and the fringe visibility vanishes."
- people .bu.edu/alexserg/PRA32106.pdf
So yeah, every time QM is impossible to intuit. Frankly, I always end up confused interpreting real life examples.
I was tripped up because it did not seem that the expected two slit pattern appeared and the classical explanation seemed a suspicious coincidence. When considering this for quantum cryptography, I think it is fair game to consider the light subsequent the eraser and between the 3m as impossible to observe without interfering with communication (ie. unhackable). See: optics .rochester.edu/workgroups/lukishova/QuantumOpticsLab/2010/OPT253_reports/Justin_Essay.pdf