See manual page perlsyn:

If any part of LIST is an array, "foreach" will get very confused if you add or remove elements within the loop body, for example with "splice". So don't do that.

UPDATE: jwkrahn is right, delete doesn't shrink the array except when it is the last element, so above manual page excerpt has nothing to do with the problem

In reply to Re: Accessing (deleting) array elements in a hash of arrays by jethro
in thread Accessing (deleting) array elements in a hash of arrays by onslaught

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