I've removed the UPNP, and manually entered all the ports I need opened. Works ok for now, I'll keep checking to make sure.
UPNP is now disabled on my router. Hopefully the feature will work better on future firmware versions.

Sorry if my comments are in the wrong place. A couple of questions; to what extent does DrayTek take of anything posted on this forum and secondly presumbly bugs are fixed through firmware upgrades but what is the best way of knowning when a firmware upgrade has been made?

yep its a bug which has been there since 3.4 firmware

update to 3.3.5.2 firmware, then in your firewall settings turn off "Accept large incoming fragmented UDP or ICMP packets" and "Enable Strict Security Firewall"

the workaround is posted elsewhere in this forum, I just cant remember where I saw it!

Interesting cbsys - thanks. I have since bitten half the bullet and am trailling a 2830 instead - do you happen to know if it's similarly afflicted?
To answer the previous question - yes they do monitor it, but don't accept things posted here as bugs, more's the pity as users on this forum are more likely to be knowledgable than anyone submitting a bug report. I think they have a mailing list you can subscribe to, but I just check the website download page monthly....