Re the line break. That was me who said it needed to be <br/> earlier in this thread, it was just twice now I have made the same mistake, sigh. And provided you put it in the correct part of the expression I don't see why it shouldn't work since it did for that previous example/user. The only "issue" I found is that when you close and reopen the dialog the formula loses the tag and instead displays the formula split across two lines, which indicates just hitting enter at that point is the other way to insert a new line in the formula as it still works fine. The being displayed differently is just because the computer is treating the formula like a web page and following the instruction to put a break in there rather than displaying it as those characters.
As for the FFDL issue, it sounds nothing to do with this plugin. You said yourself if you generate separately it works. So it must be to do with the metadata object that FFDL passes to the plugin in my opinion.