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Absence of Compile warning in Mathematica 4

When I run the program

rCMP = Compile[{x},
Module[{as = {0., 0.}, a1=0., a2=0.},
	{a1, a2} = {x, x+1.};
	as = {x, x+1.};
	(* {a1, a2} = as; *)
with and without the commented line, the times on a PPC for
rCMP /@ Range[5000.];//Timing
in Mathematica 3 and Mathematica 4 are
Mathematica 3 without: .08; Mathematica 3 with: 0.1
Mathematica 4 without: .15; Mathematica 4 with:1.9

Mathematica 4 is a little slower than Mathematica 3 for this.  But mainly, there is a factor
of about 13 slowdown in Mathematica 4 when we unpack a list.  This is probably a
reversion to uncompiled form without warning, specific to Mathematica 4. As a
workaround I use as[[1]], as[[2]],... instead of a1, a2,... .

Is this error published, perhaps along with others I should know about?

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