[mst]

I am sort of naive, though.  What is the point of such a question spam?

The question is not the actual spam. The pattern that seems to be common recently is to sign up as a new member, post a question that seems to be on topic (or a reply to an existing thread) and then come back a few hours later and add a signature with a spam link to the profile, which then shows up below the earlier posts.

We usually simply ban spam users and purge all their posts, but since this question led to a valid discussion that would have been removed, too, I just deleted the signature

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But...the cable did in fact fail!

The 17-85 IS is not the only EF lens with this kind of issue. The 24-105 L IS (1st gen) also can show flex cable failures, which in that case lead to Err 01 messages when trying to shoot with anything slower than f/4 at focal lenghts above 24mm.