In the teambuilder, if you build a Pokémon which runs two moves which alter Speed IVs, some funky behaviour can start happening. Clicking through the two moves below on a set I noticed this behaviour:
When clicking insde the "Hidden Power Fire" text box, Bronzong's Speed IV will be set to 30, and clicking inside the "Gyro Ball" textbox will set it back down to 2. This does keep the speed IV at a valid HP Fire number, however this number changes without alerting the user in any way which leads me to believe it's doing this by accident.
On top of that, because your IVs are not visible when selecting a move, it's impossible to observe this behaviour happening as it happens on the "EVs" panel while the "Moves" panel is what's visible while this number changes.
Hope what I've said is clear, just ping me if you need more info or for clarification on anything
e: This also happens for Hidden Powers that don't directly change the Speed IV from 31 (such as Ice).
e2: just to clarify and be as specific as I can: it's literally the action of "clicking" in the textbox that causes this to happen, even after both the moves have been added to the moveset. You can click back-and-forth to your heart's content and you'll see the IV jump up and down by itself on the EVs page.
BUG STATUS: CONFIRMED - TEAMBUILDER (DaWoblefet)