Makie surface not working with Observables

When I make a surface with Observables in Makie

using GLMakie

sep = Observable(.01)
xlim = Observable(5)
ylim = Observable(10)
x	= @lift(-$xlim:$sep:$xlim)
y	= @lift(-$ylim:$sep:$ylim)
z	= @lift([i*j for i in $x, j in $y])

fig = Figure()
ax = Axis3(fig[1,1])


And I change the range
julia> xlim[] = 5

It adds these straight lines from one side to the other.

How can I fix this and why does this happen?