Completing a single instance of a recurring task marks all future instances as completed

Steps to reproduce

1. Go to the Nextcloud Tasks app in the Web UI.
2. Create a new task (e.g., "Test Task").
3. Set a start date or due date for today.
4. Set a recurrence rule (e.g., "Daily" or "Weekly").
5. Check the task to mark it as completed for today.
6. Check the Calendar app or future dates in the Tasks app.

Expected behavior

Only the current instance of the task should be marked as completed. The system should either generate a RECURRENCE-ID exception for the completed instance or roll the DUE date of the master object forward to the next interval, keeping the task series active and open for future dates.

Actual behaviour

When marking the current instance of a recurring task as "completed" via the Nextcloud Web UI, the system changes the status of the master VTODO object to completed. This incorrectly marks all future occurrences of the task as 100% completed as well, making the recurrence feature effectively unusable in the web interface.

Tasks app version

Version 0.18.1

CalDAV-clients used

N/A

Browser

Chrome

Client operating system

N/A

Server operating system

N/A

Web server

None

Database engine version

None

PHP engine version

None

Nextcloud version

Nextcloud Hub 26 Winter (33.0.6)

Updated from an older installed version or fresh install

None

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

No response

Reproduce the issue in the Nextcloud Tasks Web UI with a daily or weekly recurring task, then trace the completion handling for the master VTODO and its individual occurrences. Done means completing today’s instance leaves future occurrences open, using the appropriate recurrence exception or date advancement described in the issue.