Orchestration Namespace problems...

My orchestrations stopped compiling. First I got this error:

"'': can only call or exec a service"

…for each call orchestration call shape, and a matching error saying it can’t resolve the orchestration name (although the dropdowns and intellisense,etc, appear to be perfectly capable of resolving the orchestration name – they’re all in the one project after all). If I removed all of the call orchestration shapes I got this error

The namespace '.BizTalk.Orchestrations.Service' already contains a definition for '_MODULE_PROXY_'

One for each namespace node involved. Looking at the interim files generated there is indeed an empty, sealed class called _MODULE_PROXY_ in the generated code.

This was I think, in the end, a visual studio bug.
I have my (30 odd) orchestrations sorted by type into folders. At a certain point (I haven’t established the exact conditions) vstudio starts defaulting the namespace property of the individual orchestration to the wrong namespace – instead of <orchestration>.<foldername>.orchestration, it sometimes just puts module1 in for foldername or just leaves the foldername out altogether.
Any deviance from the “right way” gives the errors detailed below. What really caused problems for me was that you don’t get to the namespace property of the orchestration by looking at the properties window for the orchestration file, but by opening the orchestration, and clicking on the whitespace in the orchestration designer, then looking at the properties window. I'd thought of a namespace problem first, but discounted it because I couldn't find a namespace property for an individual orchestration, and so assumed it couldn't be set per orch. Live and learn…