You may be able to disable your Smart Line in Preferences>Smart Guides>Transform Tools. I have mine turned off and I do not see the Smart Line. This may not be correct and I will defer to any with more knowledge in this, but it seems to work for me.
Still doesn't fix this problem, though:
Kris Hunt wrote:
Try this one: make a horizontal "live" line and, without having Smart Guides turned on, hold down Shift and try to extend one of the endpoints to make the line longer, and still horizontal. Surprise! It's impossible now! Heck, even with Smart Guides turned on, you can't use the Shift key to do that.
Edit: It does work fine if you select an endpoint with the Direct Selection tool, but not if you select the whole line with the Selection tool.
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