When one use "Group layers", it create a new layer with compositing mode "Normal". This does not mix well with "Wavelet decompose" feature. I suggest "Group layers" to look at compositing mode of the parts being grouped, e.g. just copy the first groupee's mode. Reproducible: Always Steps to Reproduce: 1. Open some image or create it and paint someting there 2. Image->Wavelet decompose 3. Select scale layers, say, from "Scale 2" to "Scale 4" 4. Press Ctrl+G ("Quick layer group") Actual Results: Image changes, "Scale 5" and "Residual" no loger in effect. Compositing mode for newly created group layer is "Normal". Expected Results: No effect on resulting imag. Compositing mode for newly created group layer is "Grain Merge", like of "Scale 2". Workaround: manually set the mode to "Grain Merge" in layer properties. With appearance of the "Wavelet decompose" filter, non-Normal layers might become more commonplace and user might run into problem even without knowing about layer compositing modes.
This will only work if all layers are of the same compositing mode. The other solution is to default to pass-through mode for quick groups, but I am highly against that as it will further confuse how krita compositing works to new users in the long run.
Then maybe grouping layers with different compositing modes should give a warning and/or set passthough?
I've played with several possible approaches, but they're all confusing. I think we'd better let this stay the way it is. If users can manage to use wavelet decompose, they certainly can be expected to be able to manage their layer stack.
Shall there be at least a warning when grouping "Grain Merge" layers? "Wavelet decompose" is easier to find in the menu than layer blending modes, so users may trigger and use it without fully understanding what it actually does. Another idea: Extend "Wavelet decompose" window to contain a piece of help, not just the sole "Wavelet scales" input parameter. This help can at least point users to look more about blending modes.