Hi, we use task coach on windows 10 offline. We thank you from Italy but if we complete an activity with the button it works, instead if we complete an activity from the window edit, the date is not respected if we choose to repeat after 1 or more months, weeks, years etc.
I understand your confusion, but this is behaving as designed.
In task coach, the way that repeat / recur tasks work is by moving the planned and due dates ahead.
So, say I mark planned start for 2019-02-01 and due date for 2019-02-05 and say that it should repeat monthly past on the previous dates. Then, when I mark it "complete" it actually does not save the completion date but just changes the planned start to 2019-03-01 and the due date to 2019-03-05. This happens the same way whether you mark something complete in the main view or the edit window.
If you marked something complete already that was not recurring, then it stores the completion date. If you then mark it to recur, it will at that time remove the completion date and push the other dates forward.
At this time, Task Coach does not have the ability to keep records of past completion dates for recurring tasks. If you want that, you can use effort-tracking or make a task-template and create a new task manually for each new one you want to track. In most cases, the record of completion is not important. For example, I have a "daily" task with several subtasks, and every time I mark it complete, it just moves all the dates ahead to the next day.
Hope that answers your questions and will make it usable for you going forward.