Here’s a repo with a demo project: https://github.com/DiawaKG/reproduction-smarthtml-grid-addfilter-incorrect-conditions
The main difference is that I’m using Blazor WebAssembly.

I think it’s only a visual bug if the state of the filter is displayed in the GridHeader as opposed to the column itself (like in your example).
You’ll see that the grid sets and applies the filter correctly – just the dropdown for AND/OR is not set correctly in the GridHeader.