It seems to me that tasks created in the android app sometimes become parent task without my permisson.
I am not sure but I think it happens when a task miss a label. It then becomes a parent task when synced with my pc.
I have just actually come here to report the same behaviour! I have created a task on the android version, it showed up at the bottom of the list, then (still on my mobile) i moved it to the very top of the list, and now the task has this tick next to it for showing / hiding subtasks - but the other tasks are not even indented! So in order to remove it i will have to move all the sup tasks out of that task which is a bit of a trouble.
thank you very much for this information, I've been able to reproduce this issue now. Moving a newly added task through the Android app somehow makes it a parent task on non-indented tasks.