Switching Tasks fails to switch branch

Hello, I'm using IDEA 2016.2 with Mercurial. I have a couple of Tasks that are associated with branches. When I switch tasks the Hg update fails. Is there some limitation to branch names? My branch names follow the pattern das-1234. The Hg update fails with "Update failed abort: unknown revision 'das'! It looks like it picked off the part of the branch before the dash.

Thanks.