ComboBox keeps the dropdown aligned to either sides of input field.
If due to content overflow e.g in a small frame input field is placed slightly out of viewport then it would be better to check the boundaries if ScreenBoundaryDetection is enabled and keep the dropdown in view and not necessarily aligned with input.

From customer feedback:

Label display style is not taken into consideration when calculating the width of the combobox e.g. if the display style is block, the label and combo should be on separate lines. In terms they should be equally wide.

However currently the combo is squashed to a minimum width.

Version: 2014.3.1024 - NET 4.0 - Visual Studio 2012 Pro

The bug occurs when checkboxes are enabled and one or more items are set invisible on the server-side (Visible=false). Checked items are not persisted correctly between postbacks. I have included a sample project to show the incorrect behavior.

Steps to reproduce to problem:

1- Start the sample project
2- The first combobox has 10 items. The first one has been set invisible.
3- Check an item
4- Click the "Select" button
5- The wrong item is checked. The checked item change at every postback

Also, the RadComboBox control should automatically select the first visible item instead of the first item of the list. The second combobox of the sample projet shows this behavior.

Thank you for looking at this issue.

Guillaume

In Lightweight rendering mode, the drop-down arrow has cursor type 'text' instead of 'default' in Internet Explorer (11).
Example:
http://demos.telerik.com/aspnet-ajax/combobox/examples/functionality/rendermode/defaultcs.aspx?skin=Default

In ComboBox If somehow focus is moved to dropdown element (e.g. when user clicks on a header, or on load more items button) then arrow keys and keyboard support won't work anymore.
It can be fixed by simply setting dropdown tabindex to say 1 and attaching ComboBox's own _onKeyDown handler to dropdown keydown too.

For the time being the following CSS workaround can be used:
CSS:
    <style type="text/css">
        .RadButton.rbSkinnedButton input {
            padding-left: 6px;
            padding-right: 10px;
            margin: 0;
        }
    </style>
ASPX:
        <telerik:RadComboBox ID="RadComboBoxDateTimeFilter" runat="server">
            <ItemTemplate>
                <telerik:RadButton ID="RadButtonApply" Text="Apply" AutoPostBack="false" runat="server" />
                <telerik:RadButton ID="RadButtonClear" Text="Clear" AutoPostBack="false" runat="server" />
            </ItemTemplate>
            <Items>
                <telerik:RadComboBoxItem Text="" Value="" Selected="true" />
                <telerik:RadComboBoxItem Text="" Value="" />
            </Items>
        </telerik:RadComboBox>

When EnableAutomaticLoadOnDemand="true" is set and no Height is specified, the first time RadComboBox is expanded only the topmost 3 or 4 items are visible.
The rest of the items become visible when they are hovered or if the ComboBox is expanded again.