Blender Version
Broken: Since it's introduction in 2.82 to current master.
The issue even appears in the release notes demo video.

Short description of error
Small bug, more of an inconsistency. The percentage goes from 0 to 1, which is decimal and not percentage, yet shows a % symbol.

This isn't how percentages work. Half way should be 50%, not 0.500%; 100%, not 1.000%. Of course the percentage symbol could just be removed and it'd be correct to have 0.5 and 1 as half and full.

This specific case is in decimating keyframes 'Remove' slider in the f-curve modifier, though maybe it happens everywhere else and I only just noticed.

Exact steps for others to reproduce the error
Open the following file:

In the graph editor, open the menu Key->Decimate (Ratio)
Confirm the operation with left mouse click.
Look at the Adjust Last Operation Panel.