I just did the same and it automatically added the .ics extension. I wonder if it is confused by your use of an email address to name the calendar file?

I tried exporting another calendar without the embedded period, which did automatically include the extensions. There is apparently a bug in the programming that needs fixing. As stated previously, the extension IS included if the file type is changed and then changed back.

a bug... the only bug I see is in windows if anything. But the file has a completely valid three letter file extension, why would you think it should have another added. I would be very upset if Windows started adding another file extension to the one had just set. Some applications have done this to me in the past. but they are in the past.

Per my original message, no extension is initially added. The extension is only added if I change the output file to another type and then change it back again. See the attached screen capture in my original message; it shows that the output file initially does not have an extension.

You should be able to recreate the problem by creating a gmail account, attaching the gmail calendar to your TB calendar, then trying to export the gmail account's calendar from TB.