If you change your working directory to cert:\, the prompt reverts back to "PS>". It appears that this is because Get-HgStatus fails. Observe:
C:\Users\rlipscombe> cd cert:\
PS> Get-HgStatus
G...
Id #1 | Release:
None
| Updated: Feb 21 at 3:34 PM by rlipscombe | Created: Dec 21 2011 at 3:28 PM by rlipscombe