Simulink assignment block writes garbage inside iterator subsystem.

I have an assignment block inside a complex model that I developed to run inside a time step. It should write a value to a 100-element array at the given index (zero-based). This is the expected behavior:

These are the assignment block parameters:

I then moved the model of which this was a part inside an iterated subsystem. Here is what I am getting:

The input U is being written to the array at the correct index, but the other elements of the array have been filled up with junk. (The "junk" in this case appears to be array values from MUCH earlier iterations before the array was re-initialized.) I note that this appears to only happen on this particular iteration; subsequent iterations overwrite the junk values at increasing indices as appropriate, but that is still leaving me with the value at the first index being incorrect.