Just wanted to add my voice to this thread, as I'm pretty sure this is happening to me as well

Installed 1.2 patch yesterday evening, had only just started getting minor lag issues on Sunday (55hrs approx play time) and the patch does seem to have resolved that. However, I too got completely owned by a frost dragon after installing the patch, when before though maybe not quite a walk in the park, was definitely doable. Possibly just a fluke but having seen this thread, now I'm a bit worried....
I'm not quite as high level as some of you guys yet - I'm a Level 19 Breton with 40% frost resistance helmet, plus 18% magic resist armour (pretty sure they both stack with my 25% breton bonus, giving me 83% in total for frost?). In the past I've been able to take a decent dragon breath hit with my health bar hardly moving at all - last night one breath and it almost wiped me out, I kept having to run and hide like a little girl while I built my health back up !
Definitely need to test this a bit more with some extended play, but seriously, if this patch has wiped out the magic resistance, this needs to be fixed and soon !