Are you using the beta version or the released version?
The beta is available at: http://beta.palringo.com
If you could let us know if this exhibits the same behaviour, that would be great. We have removed a couple of timers that accidentally got left in the released build.
Alternatively, if that doesn't fix it - is the location service disabled? That would help us eliminate whether it's access to the cell radio which prevents it from sleeping.
Thanks for the feedback.