Switching activity resets Thunderbird, making it impossible to add attachments

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

15.0

Where did you get the app from?

Google Play

Android version

16

Device model

Pixel 7 Pro

Steps to reproduce

1. Open Thunderbird
2. Select a message
3. Tap on the "reply" button
4. Add an attachment

Expected behavior

The attachment is added. More generally, Thunderbird does not exit the activity it was in.

Actual behavior

Thunderbird completely discards the draft you wrote and displays the message you were replying to. This also happens if you switch to a different application and then go back. More generally, if you switch to a different activity Thunderbird goes back to the activity it was previously in; if you were drafting a message, even without adding any attachments, Thunderbird goes back to displaying the message in the inbox and will discard your draft as if it never existed (it is not automatically saved in the "drafts" folder).

Logs

thunderbird-logs.txt

No source file or test is named. First reproduce the issue in Thunderbird for Android 15.0 using the listed reply, attachment, and app-switch steps, then trace the activity and draft handling involved. Done means switching activities no longer discards the draft or prevents the attachment from being added.