Allowing only 'flat' comments (i.e. not nested comments)

I think it is more correct to have like in the project module 'follow up', and not allowing user to create nested comments.

Example:

---
ISSUE

* comment 1
* comment 2
* comment 3
...
---

currently it is possible to do something like this:

---
ISSUE

* comment 1
** comment 3
*comment 2

...
---

So, is there a way to make it flat?