Using free attack overriding skill GCD

After using a skill, a Global Cooldown is triggered depending on the skill (for example, Air's embrace is about 2 seconds while dodge is 0.5 seconds). It is my impression that during that GCD we shouldn't be able to do anything with the exception of combining/stacking. Not even start charging a free attack.

I just found out that pressing the skill hotkey and the LMB to charge a free attack, both at once, the skill will be released and the free attack will start charging BEFORE the GCD passes.