eevee rendering issue, bug or feature?

Hey, I've been using the latest builds of 2.8 just to see what all the fuss is about but have hit a wall,

Opening a scene I have saved works fine, eevee loads up shaders pretty slowly, but it gets there in the end

(there's a fair few large image textures and complex shader node trees so i kinda expect it to load slowly, which is fine.)

the eevee render engine of course has a kind of gradually improving bit depth for shadows, AO and other effects, meaning they start grainy and noisy but quickly smooth out. this is an awesome feature, but I have either set something up wrong or Its broken.

I have 2 lights in my scene and a fairly basic character rig, both lights have very soft shadows and low Bias they also have contact shadows with high softness and low Bias and high thickness

my problem is after jumping into pose mode or changing the scenes render style (setting it to smooth shading or something) the shadows and AO effects remain incredibly noisy, as if they are no longer been updated and iterated on. its mostly noticeable in scenes with a dark "world" setting for the background... which is required to get super dark shadows with no ambient lighting.

so my question is, Have I changed some option or other to stop eevee from updating its shading to improve performance, or have I encountered a bug that others can reproduce, or is it an issue with soft contact shadows as disabling this feature seems to make the issue vanish

I know reporting non-crashy bugs is not happening yet but I really just wanted to see if this is a common issue.