I've checked back and found that this bug was introduced in versions 9.4.1 and 8.18.1 in February 2024. It's funny how often old bugs are found within a week of issuing new releases!
Thanks for reporting it. It will be fixed in the next release.
I know what you mean. A total coincidence, I assure you
At the time, I was just trying to inspect the format of .tws files to see whether they were binary or text. I'm not even sure if the current File->Open... behaviour (even if it prompts) is intended, as the only way I could coax TextPad into viewing such a file was to rename it to something like .twsx.