I was expecting that given the short time between them, and the small change the second edit was it would just have been a correction to my edit, therefore no need to get another +2 from it.
There are a number of reasons why the comment editing grace period ends. Most are documented on the main Editing meta post:
Grace period
In order to prevent a series of tiny edits from showing up in the revision history, a single user who edits a post is given a 5-minute grace period, except under one of the following conditions:
- The previous revision was a rollback.
- The new revision is a rollback.
During this period, any additional edits they make are collapsed into the same edit in the revision history, displaying only the final outcome of all their edits within that 5 minute period. The grace period ends after exactly 5 minutes, or if:
- Another user edits the post, at which time their grace period begins.
- A comment has been added to the post since the previous revision by anyone other than the editor (ignores deleted comments).
- If the post being edited is a question and an answer has been added since the previous revision (ignores deleted answers).
- The question has been closed since the previous revision.
One additional and largely undocumented reason concerns suggested edits: the grace period for a suggested edit ends when its review is completed, whether it results in an approval or rejection. As StackExchange employee animuson said on meta:
While your suggested edit is still pending review, you are in your grace period. Any further edits you make will get combined into the pending suggestion.
If your edit has already been approved (or perhaps rejected) and review has completed, further edits will create a new suggestion for review.
Note that the grace period for suggested edits is actually different from that for normal edits. The normal grace period is 5 minutes while the grace period for a suggested edit lasts until the review completes:
Your grace period actually applies to the suggested edit still being active. If it hasn't been approved or rejected yet, you can still continue to make additional edits to it which all get collapsed into that suggestion; just click the edit button again and the box will fill with the edit you suggested. Just make sure if you make any major changes you modify the edit reason so that you don't confuse the heck out of those reviewing it. I've done this before, myself, when I noticed a misspelling in some text I added.
On most of the smaller sites, it can take some time for edits to get approved/rejected, giving you ample time to correct any mistakes. However, larger sites may not get you much of a grace period for making changes to your suggestion.
A secondary (and shorter) explanation is here:
While your suggested edit is still pending review, you are in your grace period. Any further edits you make will get combined into the pending suggestion.
If your edit has already been approved (or perhaps rejected) and review has completed, further edits will create a new suggestion for review.
In your case, you can check the edit history and you'll find that each of your suggested edits was almost immediately approved by the OP.
Actually, if you look at the timestamps, your answer to the question would also have ended your grace period if it wasn't a suggested edit.
Am I just making a big deal of something "irrelevant" like +2 reputation?
Pretty much.
Is there any way this sort of "edit abuse" can be prevented or discouraged?
This isn't edit abuse as you weren't trying to farm reputation. Real edit abuse would be if you waited for the grace period to expire, then made another partial edit or, more egregiously, if you constantly made edits to the same post that cancelled each other out.
This abuse is rare because it's incredibly obvious. The people in the Edit Review queue typically catch on fairly quickly if they see the same post(s) appearing with the same user making the edits. Because it's so rare there's no real official guideline that I've found on how to handle this. But common sense says that if you happen to come across this in the future and it's clearly done deliberately, that you should reject all such edits and flag the post for moderator attention.
