The supposed reappearance of the problem was false.
When I was testing the original problem I used a URL in a WORD doc in both the new and existing users as a test. When I got this working I reported success. The 'reappearance' of the problem came when I double-clicked urls in my email client (Agent). This probably never worked as I did not test it when the WORD document test worked with the existing user. Agent has options to set to deal with urls starting with http and https. When I changed these settings to 'use Windows registry settings' the problem was solved.
So as of now the problem is resolved - again.
As a side-observation I use Tune-up utilities with a registry clean-up (among other things) scheduled weekly. It never reported any errors related to items referencing chromehtml.
gzt: Well done, that's pretty good troubleshooting.
Surprising your scheduled registry clean up didn't find the issue.
Maybe your reg cleaner requires manual scanning and approval for removal of entries like that.
The problem with the registry is that the myriad of cleaners I have run over the years always find 'problems' that need 'fixing' in the registry. Either the registry is always corrupt in some way or the cleaners find inventive ways of reporting and fixing problems.
I am also interested to see that IE10 has 2 features I most liked about chrome. Setting the startup page to about:tabs causes IE10 to show a mosaic of the most-visited sites, and IE is spell-checking this text as I type it. While I would not contemplate going back to chrome given these experiences, now I have no reason to feature-wise.