If you specify /some/path/ as the repo "URL" [sic] in the Hudson configuration,
it will clone & build your project, but subsequent builds will do a fresh clone.
If you specify /some/path then it works. This is because Hg will store

[paths]
default = /some/path

even in the first case.

Probably MercurialSCM.source should be normalized to have no trailing slash, or
the comparison to upstream should simply ignore differences in the presence of a
trailing slash.