Incorrect about the mirror image issues. The reason why the macro doesn't work properly is because a macro is read all at once and mirror images do trigger a GCD unless you have the Glyph of Arcane Power. In order for the glyph of arcane power to work so mirror images don't have a GCD, you would need a cast sequence macro to separate the casting of Arcane Power and the casting of Mirror Images. Most people will use a cast macro and then just pop Mirror Images after their first cast of arcane blast during the burn since then it will be off GCD.
Also, as far as I know from my own personal testing and others, glyph of mirror images is only a dps increase for Arcane. The cast time for glyphed Mirror Image fireball is too long and it causes it to do less dps than unglyphed.