With LabVIEW being a data flow language, it helps to think of a While Loop as having three time regions: before, during, and after.
The terminals on the left are fed by the before. Whatever gets placed there will be read once, with the exception of the shift register. The terminals on the right won't be set until the last iteration of the While Loop and won't be available to the "after" until the last iteration is complete.
Keeping that in mind, the shift register will update every iteration and send its value back to the next iteration. It will then read the same values that existed when the loop first started. So, let's look at the two possible cases. If it was originally greater or equal to one, the value of the shift register will be at least 1. The two inputs will be the same values they were originally. So they'll sum to that same value. Let's just say they're exactly 1. The second iteration the shift register will be 2. The third iteration it will be 3, and so on. At no point will that ever give you a false to the comparison to stop the loop. The other case is where it isn't greater or equal to one. It'll stop on the first iteration and feed out a false to the case structure. The loop can only stop when the comparison is false so the case structure will never reach the true case.
I want to make sure I understand your desired functionality. You have two buttons. You want to press A and get a positive current and press B to get a negative current. Between button presses, you want the value to remain what it was?
