Editing a question to make it clearer is always a good way to improve the environment of this community. But I found that, while some mistakes are made throughout editing the post, it seems like we cannot make further changes to it, and even I could not delete it. It seems like a kinds of embarrassing to see the mistake laying on the "edits" column.
And it becomes more embarrassing particularly when the edit is accepted.
Is it a problem to be solved?
It's correct that you can't suggest an edit to a post while there's another one pending. That would make reviewing a bit awkward; if both edits are approved, what would the final result be? Users with >2k reputation who are reviewing the suggested edits can choose to improve edits which need more fixing, and also reject & edit posts immediately.
You actually can improve your own suggested edit while it's being reviewed. You cannot retract it.
If this happens to your own post, you also have a shot at reviewing the suggested edit (even if you don't have 2k reputation), or to roll it back if it had already been approved.
Users who make too many bad edits will eventually be banned (temporarily) from suggesting edits. The formula for this is described here. The system looks at the number of rejected and approved edits in the past seven days; the threshold for the ban is
$$\text{# rejects} - \frac{\text{# approvals}}{3} >= 5$$
