Mouse problem (but it's not the mouse)

[Stormz]

Hi. For the past fortnight, my Mac has been driving me utterly crazy. It's mouse-related but not caused by the mouse.

The problem is this. If I drag something - say, moving a file, or highlighting over some text - it frequently 'loses grip' of it too early, even though I've still got my finger on the mouse button. This is super-annoying and only made worse by the fact that, while my finger is still held down, it sometimes regains the 'grip', so it becomes a new click and drag. Cue lots of mislaid emails and files, FTP mistakes, etc.

Also, double-clicking to highlight a word ends up coming out as either a single-click or a triple-click (which highlights the whole line of text).

It's intermittent but more often happening than not.

I use a wired mouse on a 2010 MBP running the latest Yosemite, 10.10.5.

- It's not the mouse. I've tried 3 of them, all wired. Same thing happens with each.
- It's not the mouse mat - tried different surfaces.
- It's not any one USB port - I've tried both ports on my MBP, and the keyboard ones too.
- It's not any open applications - it happens when I just have Finder open. (No login items.)
- Bluetooth is off. It's not that.
- I've played around with the System Prefs > Mouse > Double click speed. High, medium and low. It still happens.
- I've deleted the mouse prefs files like ~/Library/Preferences/com.apple.driver.AppleHIDMouse.plist and restarted. No joy.
- I've checked 'Ignore built-in trackpad when mouse or wireless keyboard is present' in Accessibility Preferences.
- I've verified & repaired permissions in Disk Utility - still happens after that.
- I've verified disk in Disk Utility - it reports that my disk is ok.
- It's not my Mac user account - I created a brand new user account, and it happens in that also.
- I've booted in Safe Mode. The problem still occurs in that.
- I've zapped the PRAM.
- I've done an SMC reset.
- I've run Apple Hardware Test (basic and extended) - no trouble found.
- I've reinstalled Yosemite 10.10 from a thumbdrive (not a clean install) and it still happens.
- If I switch from my USB wired mouse to a bluetooth mouse, the problem doesn't occur.

Based on the above, where do you think the problem likely lies?

Anyone had anything similar? Is there anything else I can try before doing a complete erase and install?

Thanks.

 

[richard2]

Hmm… perhaps your trackpad is faulty…?

 

[Stormz]

The trackpad works fine. (On the MBP I mean. I don't use an externally connected one - just mice.)

 

[richard2]

It could have a fault that's causing it to erroneously register input.

Try the following:

1. Open System Preferences.
2. Choose Accessibility.
3. In the left pane, select Mouse & trackpad.
4. Enable the option Ignore built-in trackpad when mouse or wireless keyboard is present.
5. Observe whether the issue reoccurs.

 

[Stormz]

It could have a fault that's causing it to erroneously register input.

Try the following:

1. Open System Preferences.
2. Choose Accessibility.
3. In the left pane, select Mouse & trackpad.
4. Enable the option Ignore built-in trackpad when mouse or wireless keyboard is present.
5. Observe whether the issue reoccurs.

Thanks Richard. I should have mentioned, I've already done that. Doesn't make a difference.
[Have updated original post]