A task can be tagged with multiple projects, only if the projects are not descendants or ancestors of one another. However, it is possible to add the tags of a parent and a child project in the tag field, but only the last one will be saved.
Some hint or cue that one of the tags will be removed upon saving the task.
- create a new task
- tag it with to projects which are parent and sibling
- save the task
- edit the task
- only the last project tag is present