How do I permanently delete text substitutions from System Preferences > Keyboard > Text. I have deleted them several times using the (-) key, but they annoyingly reincarnate themselves after a restart.
Indeed a severe annoyance. I spent a lot of time on the phone to Apple and no solution was achieved, only "wait". I ended up doing a simultaneous reinstallation of OS X 10.10.3 and my iOS 8 devices and this has apparently made them go away. I have since upgraded to OS X 10.11 and iOS 9 and they disappeared for several months. However, they have just come back this AM for no apparent reason on startup.
Do you have any other Apple devices? Text substitutions get shared between all of your iCloud enabled products. I had a shortcut for my email address (backslash plus the word "email") that kept triggering all over the place, because iOS and OS X "helpfully" ignored the backslash - great when I wanted to plug my actual address in, terrible when "please email that file" got turned it into "please firstname.lastname@example.org that file".
The only way I was able to kill this was to delete the shortcut from all of my Apple products in quick succession - for me that meant iPhone, MacBook Pro, and iPad. You'll need to have all devices you signed in to using your Apple ID handy to do this. You may have to do it more than once for it to "stick". Good luck.