I've seen a couple unexpected results in stories I've posted, I think due to the automated text processing. I post as HTML with all quotation marks already converted to curly.
1. If a quotation ends with a close-italic tag (as in "He said what?") the right double quote gets turned into a left double quote. This is clearly wrong and looks like a dumb typo.
2. If a work begins with an apostrophe (right single quote) (as in 'em for them or 'cause for because) the apostrophe is turned into a left single quote. This is wrong but since most autocorrecting word processors also miscorrect that to a left single quote, it just looks like bad proofreading.
3. The string of space+ellipsis+questionmark gets turned into ellipsis+space+questionmark. This isn't wrong, exactly, but it's unexpected.
There may be more I haven't noticed. But all three of those have happened repeatedly.