My sim has a Handiness skill of 10, and a significant inventory of various repair parts, so I've started having her upgrade public amenities. (She's already upgraded everything in her own home.) One of these was the fireplace in the clubhouse in the park.
The upgrades were disabled, with a popup that she couldn't perform the upgrade while the fireplace was on. But the Instant Upgrade button was not disabled. And sure enough, she reached into the burning fireplace and quickly performed both upgrades.
I would expect the Instant Upgrade button to be disabled when the upgrade buttons are disabled, or for the sim to turn off the fireplace, then perform the upgrades, and then turn the fireplace back on. The current behavior is a little off...
Edit By Crinrict: Adjusted Title to better reflect the issue
