I have seen two strange things with Iris, probably bugs, very easy to reproduce:
1. if you set a group of unit to guard Iris, Iris will then stop every 2 meters (with a hourglass icon) when asked to move. To circumvent this, you can press S a couple of times and then Iris gets his normal behavior back.
2. when a unit is under the Iris area, it is set to hold fire, which is intended. However, when the unit is set manually to free fire, while within the cloaked area, it will stay this way only for a moment, returning then to hold fire, which is annoying.