This is fixed in 1.0.53+ - I previously gave up on prefix/postfix operators for accessors after the common ones ([], [@], [$]) since you need 4 different variations of generated code, each with its own unit tests to validate stack manipulation:
So var val = my_list[| my_index]++; has to compile to
push my_list
push my_index
duplicate top 2 items on stack
call ds_list_find_value with top 2 items on stack, discard them, push result to stack
copy result (top item on stack) beyond top 3 items on stack
add 1 to the top item on stack
call ds_list_set with top 3 items on stack, discard them
pop earlier result from stack, store in local #i (val)