Chapter I: Speculations
For reference, here's Braiam's edit summary/comment:
Moving in-question answer to proper answer. Also, some styling
My speculations on why the suggested edit was rejected
The reviewer might not be aware that the block of code is an answer, or he might simply disagree with your interpretation (stated in your edit summary) that the code is "in-question answer". He might have thought it is part of the question, sort of like what the OP has tried so far. To be fair, the OP's wording leaves some room for ambiguity.
The reviewer might erroneously think that moving code from OP's question to an answer is not acceptable, even if he recognizes that code is in fact the/an answer to the question being asked, because:
he might think that no one else but the OP should take credit for that answer (if it is ever going to be posted as an answer) since it is the OP's answer.
"in Moderators we trust": the fact that a prior edit to include the answer in the question was made by a certain moderator-who-shall-not-be-named might mislead a reviewer into thinking that this suggested edit of yours is invalid. In other words, the reviewer trusts the moderator-who-shall-not-be-named's judgment more than he does yours.
The reviewer reads the edit comment, doesn't really understand it, doesn't bother investigating further (e.g. by looking at the question/answer/their comments), and just looks at the diff.
The reviewer doesn't even read the edit comment and just looks at the diff.
A close variation of this is that the reviewer sees a radical addition/removal of code in the edit, and rejects the edit in a knee-jerk response. This might be a symptom/consequence of robo-reviewing.
Chapter II: Something you can do as an editor or as one-who-suggests-edits
There's not much you can do about #2 and #4. But you can prevent (or at least alleviate) #1 and #3 by being even more verbose in your edit summary/comment. For one you can explicitly mention the comments/discussions that were made on the question.
Moved this code into a community wiki answer (https://stackoverflow.com/a/17747098/1743811) because it really should be posted as an answer. Please see the comments by ChrisF, Bill the Lizard, or Ryan Gates on the question (e.g. https://stackoverflow.com/questions/1233466/how-to-print-tiff-files-automatically#comment24693230_1233466)
Admittedly despite such heroic efforts, your suggested edit might still get rejected. But at least you can proudly declare
Um, I already gave my best, and I have no regrets at all
Chapter III: How the reviewers could have done better
I think reviewers should adopt (or be educated about) a few good practices
Reviewers should read the fine (edit) comment (if they haven't been doing so)
In case of doubt about the correctness of a seemingly radical edit (removing/adding a block of code) even after reading the edit summary/comment, reviewers should open the post in a new tab and look for clues (especially the comments on that post) to help them decide.
Chances are, if the reviewers have seen the comments (now deleted, but see Appendix C) on the question itself, they would have thought that the suggested edit is a correct one.
Admittedly, much of this (and more) is discussed in this excellent proposed FAQ titled "What are the guidelines for reviewing?", but I don't think a lot of reviewers (or users) look at it or know of its existence.
In response to possible reason #2, reviewers should also be made aware that it's perfectly fine to cut out self-answer within a question and post it as a separate answer. Here are some related Meta discussions for your viewing pleasure:
Chapter IV: How about a new button on the Suggested Edit's review interface?
I don't know if such a feature request already exists, but maybe we can add a See context button in addition to the existing Approve, Reject, Improve, Skip buttons in the review interface.
This new button would open the edited post in a new tab. Yes, you can already open the post in a new tab, but having an actual button would have a secondary effect of reminding reviewers to look at the post, its comments, and even surrounding posts if in doubt.
Appendix C: In anticipation of the "What comments are you talking about? I don't see the comments by ChrisF, Bill the Lizard, or Ryan Gates on that question. Are you hallucinating again?" response
The comments referred to in my proposed edit summary/comment above have actually been deleted at the time of writing.
But for reference, here is the content of those comments
Generally when posting code it's better to edit your question. Because there's no formatting in comments it's hard to read. In this case though post it as an answer and then accept it if it's what worked.
– ChrisF♦ Nov 12 '09 at 15:09
@Yaser: I moved the comment up to the body, but it really should be added as an answer.
– Bill the Lizard♦ Dec 13 '09 at 18:35
Note that Yaser is the OP of that question.
Please post your update as an answer and accept it. This will help future users and help you earn more upvotes/reputation.
– Ryan Gates Jun 12 at 19:52