If you enable logging you'll likely be able to get a better idea of what it is doing, but my guess is that Perform Interruption is happening before the Interrupt task is actually running.
There are a couple of ways that you could prevent it:
1. Add a wait task with a small duration to the left branch to prevent perform interruption from running before the interrupt branch is activated.
2. Restructure your tree so the interrupt branch runs first, before the branch that is performing the interruption.
3. Add a flag to the interrupt branch that gets reevaluated using conditional aborts to determine if it should run.
Have you tried creating a small test tree just to experiment with the interrupt set of tasks to see how they function? I think that this will help you get a feel for it.
Assuming the branch beneath the Interrupt task is running the Perform Interruption task will stop it from running. However, depending on the task that you have above it, that branch may start to run again (but I don't think that is happening in this case). If Perform Interruption is called before Interrupt is active it will not prevent the Interrupt task from running.