Decrement operator for strings bug in PHP?

There is an inconsistency in increment/decrement operator function regarding strings in -at least- my version of PHP. Here is what I mean:

php > echo phpversion();
7.4.11
php > $test = 'abc12';
php > // increment works as expected
php > echo(++$test);
abc13
php > echo(++$test);
abc14
php > echo(++$test);
abc15
php > // but decrement fails
php > echo(--$test);
abc15
php > echo(--$test);
abc15
php > echo(--$test);
abc15

Is this an expected behavior? Should I file a bug report or something? Do you know of a workaround?

edit: filed bug#80212

Answer

Here is what I finally went with:

function decrement($str) {
  $matches = preg_split('/(d+)z/', $str, -1, PREG_SPLIT_DELIM_CAPTURE);
  @--$matches[1];
  return implode($matches);
}

Wouldn’t call it elegant but I’d call it functional.