Bamboo not updating Mercurial sub-repositories when getting source on build server

From SAC:
"We use Mercurial and our project has a sub-repository (in a folder UI\Elegant) which is specified in the .hgsub file. The project is setup correctly, we can get it to any PC, commit, push, pull changes etc.. However, when changes to the sub-repository are made the Bamboo build fails. The hg.exe command appears to work in getting the project to the cache folder, though the sub-repository (UI\Elegant) is missing, but when it then tries to update the working folder (Bamboo\xml-data\build-dir\AIE-DEV-JOB1) it fails saying no working folder is specified for UI\Elegant.

How can we resolve this?
"
https://support.atlassian.com/browse/BSP-4674