Startup DECO app. Go to Advanced>DDNS and configure an entry if not there already. Save and then go back to DDNS settings again. Assuming the domain entered is "word1<dot>word2<dot>net" tap on "word1". It becomes selected so now try to type "word3" over it. The first letter "w" replaces the selection, but any letters subsequently typed "ord3" will be appened to the end of the existing entry, resulting in "w<dot>word2<dot>netord3".

The only way to edit appears to be a complete erase of what is there, followed by typing what you want. Although I have not evaluated this, the problem may exist in other fields too.