Sparkle update window vanishes when Sloth isn't foreground app

[m-schmitt]

On macOS Ventura 13.6.6, Sloth 3.2:

1. Launch Sloth
2. Software Update window appears, because there's a Sloth 3.3. Or, select Sloth > Check for Updates
3. Click any other non-Sloth window. Result is the Software Update window vanishes
4. Click on Slot again. Result is the Software Update window appears again.
5. Repeat steps 3 and 4.

Why does the Software Update window vanish when Sloth isn't the foreground application?

I'm thinking this is some kind of Sparkle issue. I don't think it used to do this.