in 2010 i also faced this same issue but now in 2011 its removed
so no irritation now..
I never faced that kind of issue.Can be related to a particular SP. What SP you're running currently. Did you tried to look on the knowledge base or the SPR list.
Welcome to the forum.
Are you changing the line type using the line style command in the line toolbar?
Here are a couple of links that show different methods for line changing. Which one
or which method did you use?