I have two monitors, Nexus is docked to first one and auto-hide option enabled.
When i mouse over it dock does not popup if there's maximized browser (Chrome or Firefox) with active focus on second monitor.
With Opera and IE it works correctly. So it is if dock and maximized browser are both on first monitor.

Windows Server 2008 R2
Nexus 12.2
Chrome 31.0.1650.63
Firefox 25.0.1

Well, I have to say, multiple monitor setups do have some issues.
For instance, having a full-screen programme on one monitor could mean that the widgets on a dock on another monitor stop refreshing.
If memory serves, there was a mention of that being in the pipeline for fixing, but...

App preventing activation is not in full-screen mode, it's just maximized.
And this issue occurs only with maximized Chrome and Firefox, and only when they have active focus. With all other maximized apps with active focus activation works just fine.

I can confirm dikiyvan's analysis.

I have tried various programs on the second monitor and the only one's that cause dock activation to break are Chrome and Firefox.

It is also definitely dependent on the focused window. I have a maximised Chrome window and then focus a restored Firefox (also on the second monitor) then it works fine, so simply having a maximised window isn't enough. It must be focused.

I've found another variant that causes this issue. Open up C# 2010 Express, drag on of the toolbar windows out to the second monitor and then maximise it.

I see this thread is a couple months old, but I too am seeing this issue. On my secondary monitor, when I have Chrome maximized, bumping the far left side of the screen (i.e. the side furthest away from my main monitor) does not make the dock appear. Having other applications maximized (like Explorer) does not cause the same problem. And having Chrome maximized on my main monitor with the dock on the right side of that screen instead does not cause the same problem either (works as expected).

So I don't know if the issue is with the left side of a maximized Chrome window being weird, or the far side of a secondary monitor being weird, or some combination of the two.

Is this issue still being looked into? Is there an ETA on a bugfix? I really want to buy the full version in order to have multiple docks, but this issue directly affects the spot where I want my second dock to go.