Trackpad no longer drags after Security Update 2015-003

Question

I am running Yosemite 10.10.2 on my MacPro 2010. After I installed Security Update 2015-003, I noticed my Apple Trackpad can no longer drag. Here are the symptoms:
I CAN move the cursor around the screen using the trackpad.
I CAN click, and appropriate responses occur.
If I click on a menu in the menu bar, then move (hovering) the cursor with the trackpad down the list of menu choices, they DO NOT highlight. I can click on one, and it WILL BE performed, but a submenu would NOT pop out. I CANNOT drag down the menu and to the side to bring out a submenu using the trackpad.
I CANNOT move a window or other object by tap-dragging on trackpad (double tap, holding the second tap to turn it into a drag)
I CANNOT select a phrase or paragraph by highlighting it by tap-dragging on trackpad
Hover behaviors on web pages DO NOT occur (so links that should highlight, menus on a web page that would normally drop down on their own, do not do so) if cursor is moved by trackpad.
Tool tips or other hover behaviors in web pages or outside of web browser DO NOT occur if cursor is moved by trackpad.
All behaviors are NORMAL if I use my Wacom tablet stylus to perform the same cursor move.
So, if I move the cursor over something using the trackpad, nothing happens. If I then move the cursor over the same thing using the Wacom stylus, highlighting or other hover behavior occurs.
Yes, I've changed the batteries in my trackpad, and it works fine otherwise. It does NOT skip or exhibit symptoms of a poor connection. Three-finger and four-finger drags to go to Previous Page in Safari, or switch desktops, DO work.
Only single-finger dragging is gone.
This issue occurs on my 2010 MacPro running 10.10.2, but does not occur on my 2009 MacPro running 10.10.2 at work.
Both have the Security Update 2015-003 installed, as well as all other current AppStore updates.
So Security Update 2015-003 would not seem to be the issue, but that was the thing which changed on my OS immediately prior to the beginning of the undesired behavior.
There is no setting in the Trackpad control panel that has to do with single-finger dragging. I've also checked the Mouse control panel and the double-click speed is the same between the two computers (the one where Trackpad drag works, the other where Trackpad does not work).

Answer 1

SOLVED:
This issue went away by itself after a reboot for a software installation.