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I have a 2012 MBP retina display. Over the past few days I've noticed that my trackpad has started to become finicky: it's hard to pinch, the cursor occasionally "jumps" and sometimes gets stuck so badly that it can only move on one axis (e.g., can only move left or right). After restarting and resetting VRAM things seem to momentarily be fixed: but I don't know if this is strictly power of suggestion. The fact that the cursor is stuck and that restarting helps fix the problem implies to me that the problem may be in part software related.

I've seen previous threads that suggest replacing the cable and that this was a frequent problem in previous generations of the MBP. My mac is still under warranty, but I wondered if there may be any software causes that I should investigate.

If things don't pan out, I can always take it to a store.

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Does it act the same on battery power? Or, can you switch the powersupply plug to the long bulky power cord?

If being on battery clears up this problem, then you may have a ground problem (at least, I have identified this mouse-jerk issue on one mbp). This is also the cause of the 'tingling' that is sometimes felt when you stroke the aluminium case.

A lack/failure to ground occurs under many conditions. E.g., power supply uses the direct plug rather than the heavy power cord as the direct plastic power plugs don't transmit ground. Or, there is a ground problem further upstream (dodgy power board or UPS, dodgy electrics in building). Or, something metal being touched is actually charged (scary). Or, some combination of effects.

If not grounded, the voltage inside the Mac "floats" away from ground, leading to weird effects when you touch the machine, as you are effectively a different ground competing for a different level. And, touching is exactly what you do when using the trackpad.

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The left button on my MacBook Pro (mid 2012) failed to work since this morning. I tried three reboots and nothing would get it working.

As soon as I plugged in the power cord the left clicked started working. I pulled the power cable out and the mouse button kept working.

Weird power/ground issue IMHO.

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