Drawing programs have serious limitations, especially if you want to change models or store them in Windchill. See the following articles.
(And yes, it bugs me to no end that they tell you to use ":0" in some articles and then tell you NOT to do so in other articles!)
https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS103181
https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS95046
https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS166261
https://support.ptc.com/appserver/cs/view/solution.jsp?n=114055
Here is a old discussion we had over at PTC User on this same topic.
http://portal.ptcuser.org/p/fo/st/post=118912&anc=p118912#p118912