This is really strange. The online demo works fine, thanks for that pointer.
Also if I replace the above onBeforeCellRender by
dp.onBeforeCellRender = function(args) {
if (args.cell.y <= 1) {
args.cell.disabled = true;
}
};
(as i actually want to disable the first two resources) it works fine. But with
if (args.cell.resource === "Projekte") {
args.cell.disabled = true;
args.cell.backColor = "#ccc";
}
it does not. I checked with the debugger that the if clause is true and I can also see that the backColor changes. Only the Cell disabling doesn't work here.