This was a bug caused by the fact that the keycode for left-arrow turns into '%' when cast into a char in combination with the fact that the dictionary for the autocomplete contained ALL keyword/operators rather than just the alphabetic ones.Whenever you move the caret left and it "passes" through non-whitespace a "%" appears as a viable autocompletion
Anyway, fixed now :-)
WRT ClickOnce... Wikipedia covers it fairly well http://en.wikipedia.org/wiki/ClickOnce and MuzzleFlash also explained it in detail so I don't have a lot to add but here's the way it works....
When I create the application, it is split into a small 'setup' file and then the main bulk of the application. The setup file contains a link (URL) to the location of the main application so it can be stored it a completely different location. (You can even email round the setup file or use a really old version and it will still work.)
When you run the setup file it looks in the expected location for the application and uses some metadata to figure out which is the latest version it needs to download in order to install it.
Once you have installed the application it contains some similar code to the original setup file. Every time you start it, it briefly checks the original download location to see whether a newer version is available and installs it if one is.
Apart from that it is non-intrusive and does not sit in the background checking periodically. Hope that explains it.