I have mixed feelings about this.

I'm a bit puzzled by it.
The "A*" format apparently removes trailing whitespace, but not embedded whitespace:

D:\>perl -wle "print '#' . unpack('A*', 'abc   ') . '#';"
#abc#

D:\>perl -wle "print '#' . unpack('A*', 'abc   d') . '#';"
#abc   d#
[download]

How is all of that explained as being "expected behaviour" ?
Duh - it's explicitly stated in the documentation - " When unpacking, "A" strips trailing whitespace and nulls".

Cheers,
Rob