Order of @animate and @layout in Julia

I want to ask about the mechanism of the following errors. The code

lay = @layout [a{0.4h}; grid(2,2)]
@animate for...
plot(..., layout = lay)
end

in Jupyter produces an animation with only one frame (the rest of frames are blank). There are no error messages in Jupyter.

The code

@animate for...
lay = @layout [a{0.4h}; grid(2,2)]
plot(..., layout = lay)
end

works fine. Why? Isn't this inefficient?