Select a rom folder in the tree and let's assume that it contains several green files and a few reds. When selected, the files appear in the left panel. Select one of the files (a green one) and see its contents appearing in the right panel. Now, in the left panel, click on the "green" filter over the list, so that the green files are removed. Along with that, no file is selected in the left panel now. In the right panel though, the selected file is not cleared. It still shows the last selected file.
This is not an actual problem at the moment, but it has the potential to become one in the future. It would be better to clear the right panel if no file is selected in the left one (probably after the application of any of the filters).