Yup....Potable-Aqua in a poly zip bag will degrade into an inactive tablet quite quickly and potentially damage adjacent items in the kit with iodine vapors.
In a kit this size I would simply carry the Potable-Aqua bottle they are supplied in....gives you 25 doses and shelf-life at the same time.
Switching to micropur is another alternative, but I just carry a full bottle of Potable-Aqua in my shoulder bag kit.