When keys in associative arrays are only composed of integers, the concerned lines of the table are converted to non-associative lines, after passing through array_merge(). With keys composed of strings or mixed integers-strings, this misbehaviour doesn't occur.

$array1 = array ("foo" => "bar", "bla" => "blabla");
$array2 = array ("123" => "one two three", "456" => "four five six");

while (list ($key, $val) = each ($array1)) print "$key : $val \n";
  /* this returns :
foo : bar
bla : blabla
  it's correct */

while (list ($key, $val) = each ($array2)) print "$key : $val \n";
   /* this returns :
123 : one two three
456 : four five six
  it's also correct */

$array3 = array_merge ($array1, $array2);
while (list ($key, $val) = each ($array3)) print "$key : $val, ";
   /* this returns :
foo : bar
bla : blabla
0 : one two three
1 : four five six
   strange, isn't it ? */

Note: I've installed mandrake-cooker rpm's of php4, as the rpms shipped with redhat 6.2 are only old 3.something. Perhaps this can be the cause of the problem ? I haven't tried to reproduce the bug on another system.