Sounds like a bug.
I would suggest upgrading to the latest version, 12.1.4.1 to see if that corrects it, otherwise you can contact support.
IPS is compatible on servers but you need to be careful as it's only a software IPS. Is this a HA/high bandwidth server? If so, you may need to remove the IPS component. This article explans it:
http://www.symantec.com/docs/TECH162135