even though I have specified "email" as the default reminder option "push notification" is selected by default whenever I add a reminder to one of my tasks.
In the "settings" area where you choose your default reminder, that is for relative reminders, a default of 30 minutes before deadline. When using the settings button beside the task, and choosing "reminders" those are absolute reminders.
They are two separate features and that is why that setting appears to not work but it is.
We will consider adding a default reminder setting for absolute reminders in the future.
You can create that request in our votebox: