If you try to load a file that is invalid JSON (or not JSON at all), the name of that file gets "stuck" in the filename field, and uploading a second, valid JSON file results in the two names being concatenated. (If you upload a second invalid file, it gets "stuck" too).
Confirmed on both Firefox 51.0.1 (64-bit) and Chrome 56.0.2924.87 (64-bit) on macOS.
If you try to load a file that is invalid JSON (or not JSON at all), the name of that file gets "stuck" in the filename field, and uploading a second, valid JSON file results in the two names being concatenated. (If you upload a second invalid file, it gets "stuck" too).
Confirmed on both Firefox 51.0.1 (64-bit) and Chrome 56.0.2924.87 (64-bit) on macOS.