Auto adjust colors not working

[J.A.G.]

When in any image I press *Shift-U* or do *Image > Auto adjust colors*, nothing happens. Undo is inactive, so nothing has changed.

Have I changed something unwittingly? Or is something else to blame? Does anyone know how to correct this?

Thank you.

[Leif]

Options | Properties | Misc. 1: Use Undo... not ticked?

[J.A.G.]

Ìt's not Undo that is not working properly, but Autoadjust colors. I mentioned Undo only to show that nothing happens when applying Autoadjust.