Occasionally, I will press Ctrl-x and Ctrl-a to increment/decrement the highlighted number, and the opposite operation will happen.This usually happens when I'm working with with registers (q).  Could I possibly be setting up some sort of alias between the two commands?  How do I fix it besides opening/closing vim?
Ctrl-A and Ctrl-X seemed to be switched sometimes!
key bindings
Nevermind, the number I was incrementing was in a date time (like 2015-08-07) and I think vim was interpreting it as a negative integer.D'oh.