Bug? Odd behavior of [a b/c] with results from mean().

[Michael K-K]

First I used build in L1. Then a list {} directly put on stack.
I further recognized this:

1) mean({1, 2, 3, 4}) -> 5/2
2) mean({1.0, 2.0, 3.0, 4.0}) -> 5/2
3) mean({1, 2, 3, 4, 2.5}) -> 2.5

1) + 2) the [a b/c] does nothing, 3) [a b/c] works as expected. No problem with median and [a b/c] in all three cases.