I'm curious if there's anyone who has encountered this problem with blurring deep shadow maps and/or can shed some light on the issue.

When using particularly low-res deep shadow maps, regardless of smap pixel samples, it seems that low to mid range values of blur cause or accentuate banding type artifacts (or striations along the geo).  If the blur value is cranked up higher it eventually takes care of the problem, but it's unlikely you'd want blur values that high all the time.  A bias of 0.2 doesn't resolve the issue.

I notice this behaviour using maya lights, and maya lights with 3delight shaders (spotlight) and our own internal shader.

Currently, I'm getting better blurring results by lowering the map resolution even further and increasing the samples to smooth it out. 

From other threads I gather that using blur isn't necessarily a bad thing.

I'm interested to know if this is a common issue, and easily overcome.  And also, if anyone can explain what's happening under the hood when this is happening.

thanks.