Under certain circumstances, mis-ordering of certain formatting tags will break all formatting on the forum thread for the remainder of the page.
This can occur when {quote} tags are opened before a spoiler, and then closed inside of a spoiler - at least when it happens at the end of the post. For example, the following sentence (if used with square brackets) should impact all further formatting on the page...
"{quote}This will {spoiler}break the forum's formatting.{/quote}{/spoiler}"
Examples of this happening can be seen in these three posts.