Settings > System > Storage in Windows 10 shows incorrect values

If I open Settings in Windows 10, then go to System > Storage, I get the following usage for C:

161Gb used of 285Gb

whereas File Explorer gives the more sensible 21Gb used of 145Gb, which is almost certainly the correct values, given that it is a 145Gb partition, and is a fresh install of Windows 10.

Can anyone shed some light on this mystery?