I normally hesitate to post my thoughts in such learned company, but here goes. 
under Win32
perl test.pl  QUICK=BROWN\ FOX JUMPED=OVER\ THE\ LAZY DOG

produced an @ARGV of

$ARGV[0] = 'QUICK=BROWN\\';
$ARGV[1] = 'FOX';
$ARGV[2] = 'JUMPED=OVER\\';
$ARGV[3] = 'THE\\';
$ARGV[4] = 'LAZY';
$ARGV[5] = 'DOG';

So to achieve the result required I tried

my $line = join ' ', @ARGV;
$line =~ s/\s(?=\S+=)/\t/g;
@pairs = split(/\t/, $line);
%defaults = map {/([^=]+)           # everything up to the = sign into
+ $1
                       =            # the = sign
                       ((\S+\\\s)+  # all words followed by "\ "
                       \S+)         # word after the last "\ "
                       /x?($1=>$2):()} @pairs;

for ( keys %defaults) {
  print $_,"=",$defaults{$_},"\n";
};

which produced

QUICK=BROWN\ FOX
JUMPED=OVER\ THE\ LAZY

[download]
Ay_Bee 
-_-_-_-_-_-_-_-_-_-_-_-
My memory concerns me
- but I forget why !!!

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In reply to Re: Regular expression double grouping negation headache by Ay_Bee
in thread Regular expression double grouping negation headache by JayBonci

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