Undo options in Affinity Photo

[Krishna Prasad Kotti]

I am using Luminosity masks and Layers.

When ever I am a change in the Layers like curves. I add a curves Adjustment layer. I modify the curves. Make two modifications change Midtone and Highlights. I cannot do undo to revert the last change.

Same issue in Luminosity Masks Layer, I cannot undo the changes, I have reset option but cannot do undo with command z

Is this normal, I wish we can undo a small changes done in the curves not reset the whole curves adjustment.