Building in mock vs building outside of mock

[PFJ]

Hi,

This has puzzled me for most of yesterday (I had the weekend off doing
anything!)

I have a couple of C# packages in BZ. Outside of mock, they build
without a problem at all - when I inspect the packages, the contents are
correct and everything is in the correct place.

When I build it under mock, the build fails with an error that a
particular directory is missing (it varies as to which depending on the
package being built).

Why does this happen? What is so different to mock as to building
outside of mock?

TTFN

Paul
-- 
"Logic, my dear Zoe, is merely the ability to be wrong with authority" -
Dr Who