Why this 1-liner doesn't work as its non 1-liner version?

Question

I have the following code:

f_classes_memberships = {f_set: -1 for f_set in F_SETS}
for theta_set in THETA_SETS.keys():
    for omega_set in OMEGA_SETS.keys():
        f_classes_memberships[FUZZY_TABLE[theta_set][omega_set]] = max(f_classes_memberships[FUZZY_TABLE[theta_set][omega_set]], min(theta_memberships[theta_set], omega_memberships[omega_set]))

which correctly gives me the result:
{'PVVB': 0, 'PVB': 0, 'PB': 0, 'P': 0.5, 'Z': 0.16666666666666666, 'N': 0, 'NB': 0, 'NVB': 0, 'NVVB': 0}

But, if I replace it with this code:

f_classes_memberships = {f_set: -1 for f_set in F_SETS}
f_classes_memberships = {FUZZY_TABLE[theta_set][omega_set]: max(f_classes_memberships[FUZZY_TABLE[theta_set][omega_set]], min(theta_memberships[theta_set], omega_memberships[omega_set])) for theta_set in THETA_SETS.keys() for omega_set in OMEGA_SETS.keys()}

then, I get:
{'PVVB': 0, 'PVB': 0, 'PB': 0, 'P': 0, 'Z': 0, 'N': 0, 'NB': 0, 'NVB': 0, 'NVVB': 0} which is not the correct result.

I looked into it with the debugger:

• During the for-loops, the max() function yields the correct result, but the dictionary f_classes_memberships contains just values of -1 and doesn't change at all (even though it should).
• After the execution goes beyond that line, then f_classes_memberships is full of values of 0, as specified below the problem code.

Here is a richer part of the code, in case you need more context.

• The part mentioned here is between lines 111 - 118.
• If you want to try it, then comment/uncomment the lines 115-118 to switch between the code that works and the one that doesn't.