Changing opacity unset default fill color in shape tools

Steps to reproduce:

• reset/delete preferences
• open Inkscape
• switch to rect/ellipse/star tool
• draw a shape
• change the opacity
• draw another shape

What happened?

• the default style's fill color is changed from blue to unset

What should have happened?

• fill should stay the same on opacity change

Version info

• Inkscape 1.2-dev (e73f3c57b0, 2021-07-18) Linux Mint 20
• alpha0 appimage has this too
• 0.92.5 doesn't experience this since shapes have unset fill by default.