4.3.2.5 has just been released on draytek.com, however it doesn't fix the issue.

I've e-mailed support, as I've just picked up on that they said it would be fixed in 4.4.3.
This has been released for other routers, I've asked to clarify if this was a mistake or intentional.

UK support is unfortunately not great. They're obviously trying to weed out user error, however I think they're a little too good at their job!

Update: 4.4.3 should be the next version.