Why `LAPACK.trtrs!`, not `BLAS.trsv!`?

On a related topic, do you know why I get this warning:

julia> n = 10000; A = randn(n,n); b = randn(n); BLAS.trmv!('U', 'N', 'N', A, b);
WARNING unrolling of the trmv_U loop may give wrong results

I googled for that warning but nothing came up.