I have this too, but I have found a workaround to it, although twice it worked straight away, the other times it took 2 or 3 attempts.
Anyway the work around I am using is to change the pace alert to be a target instead of a range and then set the target pace to be what you want the upper limit to be. Then back out of alerts, go back in, change target back to range and it should have set both the upper and lower limit to whatever you set as the target pace. You can then change the lower limit to whatever you need.
As I said, sometimes it works straight away, others it takes a few attempts, but I have always got it to work
Hope that helps