Statement not respecting if expression [list]

So i have this code:

if index < 13:
    b_list = a_list
    print('True')
else: print('False')

but it seems that even when index IS > 13 it still run the statement 'b_list = a_list'. I get this output:

True
index: 12
cfr_l_rle: [1, 1, 2, 4, 1, 3]
cfr_l_rle_2: [1, 1, 2, 4, 1, 3] # everything works fine

False
index: 13
cfr_l_rle: [1, 1, 2, 4, 1, 4]
cfr_l_rle_2: [1, 1, 2, 4, 1, 4] # i should get this result: [1, 1, 2, 4, 3]

Why does this happens?

How can i make it respect my if conditional.

Thanks in advance.