Problem with Lake Script in IE9

[Sempervivum]

Hallo,
on one page of my Website I'm using a lake script which mirrors an image an simulates waves floating. This is running fine in Firefox but in IE9 one problem is left: When I reload the page the animation doesn't start. Only when I press "Back" and "Forward" it is displayed. A test page containing the lake script only is running fine. I inserted alerts in the lake script:

        ca.style.display = "inline";
        ca.style.visibility = "visible"
        alert ("Timer starten " + img_loaded);
        window.setInterval(function() {
            alert ("triggert");
            if (img_loaded) {
                if (!settings.image) {
                    c.putImageData(frames[frame], 0, 0);

Both trigger, thus the script is started, the timer is started and triggers. img_loaded is true.
Any help is appreciated.
The author has kind of forum but questions there are not replied for months.
Best regards - Ulrich

[Sempervivum]

PS: Forgot the URL:
http://www.ulrichbangert.de/heimat/index.php
Testpage with lake script only:
http://www.ulrichbangert.de/heimat/index_lake.php