cphalcon: [BUG, v.3.1.2] Inconsistent behaviour of Phalcon\Config::merge() across minor versions of PHP7

Phalcon\Config::merge() of the same version of Phalcon (v3.1.2) behaves differently on PHP versions 7.0.14 and 7.0.17.

PHP v7.0.14

$config = new Phalcon\Config([
    'a' => [
        [
            1
        ]
    ],
]);

$config->merge(new Phalcon\Config([
    'a' => [
        [
            2
        ]
    ],
]));

Expected and Actual Behavior

$config is:

Everything is correct.

PHP v7.0.17

The same code results in the following $config value:

I expect $config to have the same value that’s produced under v7.0.14.

Details

• Phalcon version:

Version => 3.1.2
Build Date => Apr  6 2017 21:22:10
Powered by Zephir => Version 0.9.7-1fae5e50ac

• PHP Version: 7.0.14 vs 7.0.17
• Operating System: Ubuntu 16.04 64bit
• Installation type: Compiling from source
• Zephir version (if any): 0.9.7
• Server: Nginx