Please test it by adding <active>false</active> to your liferay-portlet.xml and redeploy it. I think it should be inactive after deploy based on. If not, just open a ticket in JIRA as this case it could be a bug, but it needs further analysis.
Based on the DTD it should work:
1<!--
2Set the active value to true if the portlet is active and available to users.
3If set to false, the portlet will not be active or available to users. The
4default value is true.
5
6This value can be changed at runtime via the Admin portlet.
7-->
8<!ELEMENT active (#PCDATA)>
