The HtmlPlaceholde does not respect the applied Scale Transformations.

The control is misplaced if it's inside a GridRow/Column and there's the browser zoom is different than 100%.

The fix will be available in the Q1 2015 Official Release.

The control is misplaced when you zoom in/out the browser window.

To work this around you can manually calculate and set the top and left positions of the HTML presenter. 

this.htmlPlaceholder.Loaded += (sender, args) => { this.htmlPlaceholder.LayoutUpdated += htmlPlaceholder_LayoutUpdated; };

private void htmlPlaceholder_LayoutUpdated(object sender, EventArgs e)
{
    this.Dispatcher.BeginInvoke(delegate
    {
        double controlTop = GetTop();
        double controlLeft = GetLeft();
 
        htmlPlaceholder.HtmlPresenter.SetStyleAttribute("top", controlTop + "px");
        htmlPlaceholder.HtmlPresenter.SetStyleAttribute("left", controlLeft + "px");
    });           
}

When placed in scrollviewer and browser is resized in order to appear the scrollbar, HTMLPlaceHodler doesn`t render correctly. The issue can be reproduced in both scenarios - setting the HtmlSource or SourceUrl property.

MouseWheel does not work when setting an HtmlSource.

Reason for declination: 
The feedback item is declined due to duplication with the one below:
http://feedback.telerik.com/Project/143/Feedback/Details/112811-htmlplaceholder-mousewheel-does-not-work-when-setting-an-htmlsource
Please follow it instead.  

The placeholder disappears if it's in a RadPane and you close another RadPane

When displayed inside a RadWindow, if the window is moved outside the browser, the placeholder gets cut off.
This issue also appears if initally the left side of RadWindow is positioned outside the browser.

The RadHtmlPlaceholder control gets misplaced when displayed inside a RadWindow in a zoomed browser. The issue can be reproduced in the HtmlPlaceholder WindowIntegration demo example.

The control doesn't work in Safari

Does not display properly when placed in StackPanel.

Currently, RadHtmlPlaceholder is an IFrame which is being rendered on top of the Silverlight plugin. Therefore, no mouse or keyboard events are being fired.

RadHtmlPlaceholder does not respect the EnableAutoZoom property.

"Value does not fall withing the expected range" exception is thrown when displayed in a tooltip in a RadMap

SetProperty fails on HtmlPresenter.

When PDF is shown, setting visibility to collapsed makes the web page blank

MouseWheel does not work when setting an HtmlSource.

When the HtmlPlaceholder is placed in an ItemTemplate of a ListBox and if the HtmlPlaceholder.KeepContentInMemory is set to True, the control is rendered twice - in the ListBoxItems and in the top left of the page

Incorrect rendering under Mac and Safari

OnUnload/OnBeforeUnload do not fire after changing SourceUrl