As Douglas said earlier, browsers try to clone previous tag when customer starts a new paragraph on an editable page. The discrepancy occurs when browser has nothing to depart from – e.g. when initially the page body is empty. In this case different browsers behave differently: IE starts to wrap every string into <p> tag, Chrome wraps each line in <div>.
To increase cross-browser experience, WebKit developers have introduced the DefaultParagraphSeparator command. You can use the following JavaScript on page loading for Chrome to change default paragraph separator to <p> tag:
document.execCommand('defaultParagraphSeparator', false, 'p');