bueno, si ahora entiendo bien tu quieres un apartado que explique por qué del bug, con material oficial...

bueno
http://wowwiki.wikia.com/wiki/Frost_mage

en el link anterior:
"In the 3.3 patch, an effect was added to the Deep Freeze talent, which now causes significant damage against a single target if that target is immune to stun (including most dungeon and raid bosses). When used alongside Fingers of Frost, Shatter, and Cold Snap, it is possible to produce short, very powerful bursts of damage."
Lo que significa que Shatter deberia darle critico a Deep Freeze (en mi caso lo use de forma simple varias veces, sin tirar un spell antes para acompañar y tampoco criteaba)

En cuanto a tu duda del efecto de lanzar 2 poderes en un objetivo congelado, voy a poner una guia:
http://www.mmo-champion.com/threads/...o-Frost-Basics
(en el segundo titulo, post donde dice "Rotacion")
"Frost rotation was never very complicated, ad not much has changed, but if you’re not familiar with the new mechanics, things can be overwhelming.
Priority for spells will be Deep Freeze > Brain Freeze > Frostbolt
You, like other Mage specs, will spam your main nuke, the Frostbolt. What happens is when you get a Fingers of Frost (FoF) proc, things can get a little more interesting. This is where Deep Freeze comes in and ends up hitting like a truck. More Often than not, you will already be mid cast for your next Frostbolt (FrB) when FoF procs. This is because the proc occurs when the Frostbolt hits your target (and why hit is so important!). Finish your cast and charge up another; one FoF is already eaten at this point. As soon as you finish casting your second FrB, you will then cast Deep Freeze (DF). This is only done if the Ghosting ability for FoF still works.

• What ghosting FoF means is you can use an instant cast directly after using the second charge of your FoF proc, effectively applying 3 charges to your spells. Doing so will increase the crit chance of all spells cast by 50% and allow for you to use DF, your 30 second atomic bomb.
If this feature no longer functions as described, you will simply cast DF immediately after you finish casting that FrB that will eat your first charge.
Furthermore is dealing with Brain Freeze (BF), not to be confused with Deep Freeze. When BF procs, you simply cast it immediately once you finish casting your last spell. This isn’t true however if you have FoF proc’d and DF is useable. "

cualquier otra guia de escarcha te dira lo mismo en pve y en pvp (solo que en pvp no usaran de ejemplo el deep freeze, sino el Ice Lance, para el clasico de clasicos "Shatter Combo".