When you do this:

 map { whatever } @array;
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you are taking the initial contents of the array as a list (that is, making a list based on the initial array contents), and map iterates over that list. If anything happens within the map block to change the number of array elements (adding or removing), this has no effect whatsoever on the initial list that drives the map iterations. Consider:

perl -le '@a=qw/a a/; map{push @a,"A"; print "@a"} @a'
# prints:
a a A
a a A A

perl -le '@a=qw/a a/; map{@a=(); print "@a"} @a'
# prints two blank lines
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But when you do this:

foreach (@array) {
    # add or remove elements in @array...
}
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you are asking for trouble. Some variations on that theme might "work" (though maybe not in the manner you intended), but in general it's a bad practice.

Don't use "for" to iterate over an array if you plan on adding or removing array elements within the loop. Use "while" for that (and be really attentive about making sure you provide the right exit condition(s) to get out of the loop).