I put the option ui_one_instance to true and opened a file. I opened another application fullscreen (Total Commander) and started the editing of a second file with CudaText. The file is opened by CudaText but the window is not put to the front to make the file visible. In my case Total Commander stays on top so it looks like the editing of a second file with CudaText is not working.
Please make CudaText the top-most application when a second file is opened via the command line.