Port forwarding problems

[#1]

I have a standard technicolor router and have set port forwarding on ports 80 and 443 to my windows homeserver for remote web access. I worked fine originally but a couple of major outages and router updates have meant that I had to keep re-applying the forwarding. The other day I noticed it wasn't working again (I don't use it very often) and when I went into the router settings the forwarding was gone - have plusnet been interfering with my router settings? I set it up again and it worked for a couple of minutes and then stopped working again - usually with certificate or 404 errors. This keeps happening but I noticed that if I set DMZ to the server all works fine. This suggests to me there is something wrong with the forwarding. Is it possible the router is at fault as it doesn't forward properly after a minute or two or might it be something else? I have tried a router reset but that didn't sort it.
Thanks
PT

[#2]

just done a hard reset and set device (homeserver) to use HTTPS Server application forwarding (instead of setting forwarding by creating new game/application. Worked for a couple of minutes and then no access again. Can routers fail to forward properly like this if they are failing? DMZ means it works all the time so not sure what's going on.

[#3]

Hi there,
Not sure what's going on but you might get some clues from a fairly in depth post by Matt here:
http://community.plus.net/forum/index.php/topic,110862.msg953864.html#msg953864
Most of the relevant stuff is in the quoted section however there's a description of how the saving of settings works that might help too.