Scott,
unfortunately there is no other custom JavaScript code.
However, when I tried to debug the problem and added onload handler to the web resource HTML's body tag, I noticed it's has been called on every navigational change (regardless if I navigate to this form or to something else), thus effectively "wiping out" the run time content I set during the Form's OnLoad.
So, in essence, I know my WR is reloaded with every navigational move, yet the primary Form's OnLoad method doesn't fire (and yes, why should it).
Now, how can I prevent WR from being reloaded (it's really not need to)?