Okay, there seems to be some misunderstandings here, so let me explain how this works. First of all, the result you encountered is not a bug, it works as it should be. Everyone knows that the specialist with a lower combat priority activates first. So let me construct a scenario here.
Lets say player A sends a sub with a Double Agent onboard from Outpost A to Outpost B. We will call this sub, Sub A.
In response, player B sends a sub with a Saboteur + 100 drillers onboard from Outpost B to Outpost A. We will call this sub, Sub B.
When Sub A interacts with Sub B, the following occurs:
Specialist phase is before the Driller phase of combat. So, the specialist with the lower combat priority takes action first. Which is the Saboteur on Sub B. So, the saboteur does his job, the incoming sub (Sub A) reroutes back. Which means, now Sub A is going from the combat point to Outpost A, from which it was actually launched.
Now, the important note to consider here is: Unless the specialist we are talking about is Double Agent or Assassin, the specialists act independent from each other. Saboteur doesn't stop Double Agent from playing his role. So, now since the Saboteur played his role, let's see what the Double Agent does:
First, Double Agent destroys the 100 drillers at the Sub B. Then, the subs swap ownership. Which means that Sub A, which was under the control of player A, is now under the control of player B. And the Sub B, which was under the control of player B, now belongs to player A. And then the combat ends.
What is the conclusion? We had already shown that Sub A is now going towards Outpost A. What happens to Sub B? Well, originally it was going from Outpost B to Outpost A. And since nothing affected his direction, The sub continues to move towards Outpost A as well. As you can see, both subs are now headed towards Outpost A. The only difference lies in the fact that now player A has a Saboteur and player B has a Double Agent, which is sadly headed towards an enemy base, and it will most likely be switched once more to player A after player A sends a sub of 1 to trigger the effect, otherwise it will get captured at outpost A.
Imagine how stupid the average person is. Then realize that half of the people are even stupider than that.
-George Carlin