Hey,
I noticed the "new unread post" star-shaped indicator in the My Content page apparently gets triggered when somebody votes on a poll in a thread I've participated in. As far as I can tell this is a bug, and would only be worthy of the indicator for the thread creator at best.

I'm not 100% sure this is the actual cause, but it only occurs on the Game genres, what do you want to develop? thread which happens to have a poll, so I'm thinking that's where the problem lies.

Or maybe I'm just a little bit obsessive about having all posts marked read is it expected behaviour?

Yes this is expected behavior although I've been waiting for IPS to address the issue of the confusing nature involved with poll vote bumping. Poll threads can have two types of interactions - someone can vote in the poll and someone can respond to the discussion of the poll - or they can do both. The problem is that when someone only votes the system makes people think there's a new response to whatever discussion is accompanying the poll since it stars the thread when it bumps it. Turning off vote bumping isn't very fair for polls as it would require actual discussion (thread postings) for it to remain visibly "active" in the forum index. Poll creators might feel the urge to post to bump their polls and thread bumping isn't allowed in general.

Turning off vote bumping isn't very fair for polls

I'm not sure that leaving it on is very fair to discussion postings. The number of times I've noticed that an idiot-thread keeps jumping to the top of the list when people vote on it, is quite high.

Thankfully, we've don't have that many polls outside the lounge, so I guess it's not a huge deal.

I'm not sure that leaving it on is very fair to discussion postings.

You make it sound like polls are in some way worse or not as good as discussion threads, which I don't get. Both are valid ways of interacting on this forum IMO and the only issue I see is the confusion surrounding the "last poster" when a poll is voted on, not that a poll is being bumped with a vote. Inane/useless polls should be closed just like inane/useless threads should be

You make it sound like polls are in some way worse or not as good as discussion threads, which I don't get.

I'm afraid that I've never seen any values to polls on internet forums. Polls are for collecting statistics, and in general statistics are only meaningful if you have very tight control of the sample population (which we don't - GameDev is a mix of everybody).