Never - I don't think they will ever fix this. Why? I have no idea.
I have turned cartwheels trying to fix the problem, to no avail. I have submitted the problem, with full documentation, to the Bug Reporter group - first in August 2015 and several times thereafter. I heard back from them in late November 2015 - not with a solution, but with a request for more information, which I sent that day. Three weeks later, I got another request (that I run a sysdiagnose and send it to them) which, again, I did. The response: none. When I first tried the various trackpad updates and etc., I got error notes indicating they could not be installed on my system. At that point, I was running OS X 10.11 'el Capitan.' So, I downgraded to OS X 10.9.5 Mavericks (13F1603) in hopes of rendering the updates installable. This didn't work either. My machine is a MacBook Pro, Retina, 13", late 2013. Processor: 2.8 GHz Intel Core i7. Memory: 4 GB 1600 MHz DDR3 Graphics: Intel Iris 1536 MB. Originally, I had the problem when I 'upgraded (?)' to Yosemite. I had hoped that upgrading again, to El Capitan, would help. But the truth is, nothing has helped. Apple knows about the problem, but has done nothing to solve it. I'm beyond frustrated.