Is it possible to install it without overwriting Opera 10?

Tried installing in a separate directory, but got an error message that opera.dll was missing.

When I today opened Opera 10 (by clicking the shortcut) the installer for Opera 11 suddenly started. After I hit Cancel, Opera 10 started as usual.

Oslo gone evil?

It only happened once.

After some experimenting I got the message "error initializing opera: module 10" instead of the previous one about opera.dll. Next I tried installing Opera11 over Opera10, same result. But when I then clicked the shortcut to launch Opera10, Opera11 suddenly came alive. Finally I renamed the "Opera10" directory to "Opera11", and reinstalled Opera10 in a new "Opera10" directory. This appears to work so far.

Now I double-clicked an HTML document in my file system. Normally that would start Opera 10, but instead the installation program for Opera 11 began, and overwrote Opera 10.