terrible bug in Mathematica (//N), but why????

Evaluating (using //N) two exact same expressions, gives wrong answer unless
fullsimplify is used first, I spent 2 days on a problem thinking my answer
was wrong, but turned out Mathematica 5 was giving me buggy answers, I
debugged it to this point, but WHY in the world is this happening? Please
help!!!

cut and paste below to see the test case:

In[243]:=
\!\(\(Cosh[\(43\ \[Pi]\)\/\@2] + \((1 - Cosh[43\ \@2\ \[Pi]])\)\ Csch[
43\ \@2\ \[Pi]]\ Sinh[\(43\ \[Pi]\)\/\@2] // FullSimplify\) //
N\[IndentingNewLine]
Cosh[\(43\ \[Pi]\)\/\@2] + \((1 - Cosh[43\ \@2\ \[Pi]])\)\ Csch[
43\ \@2\ \[Pi]]\ Sinh[\(43\ \[Pi]\)\/\@2] // N\)
Out[243]=
\!\(6.551787517854307`*^-42\)
Out[244]=
\!\(\(-1.9342813113834067`*^25\)\)



thanks,




.

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