If you are picking your curves in the offset tool, DO NOT PAN!!! It will remove your selection forcing you to re-pick!
Another issue I have noted is dimensional constraints applied to lines that still hold the offset constraint fail! I have two screencast videos for this... Here is the issue with the constraints:
https://knowledge.autodesk.com/community/screencast/9f519191-d278-45e1-8ab3-e4b0756ca02c
grrr...