radcombox's Item is binding perfectly but not displaying all on first click

Question

I am using telerik radcombobox in my project.Let me show you its mark up first..

<telerik:RadComboBox ID="cmbx_AltUoM" runat="server" Width="100%" Filter="Contains" MarkFirstMatch="true" AutoPostBack="False"
OnClientDropDownOpening="onUoMComboItemRequesting"> </telerik:RadComboBox>

Now when I am clicking on the combobox its showing this:

But while I am clicking on the lower arrow of the pane , its showing all item.

Now second time when I am clicking, it's showing all items..

Could anybody tell me why this is happening here?Please, I need help :)

Edit : while inspecting I got this (while clicking first time)

<div id="ctl05_rw_UoMGroupDetails_C_rgv_UoMDetails_ctl05_rw_UoMGroupDetails_C_rgv_UoMDetails_ctl00_AltUoMID_cmbx_AltUoM_DropDown" class="RadComboBoxDropDown RadComboBoxDropDown_Office2010Blue " style="width: 105px; display: block; top: 0px; visibility: visible; transition: none;">

div class="rcbScroll rcbWidth" style="height: 21px; this causing problem, I need to remove height attribute from here..

Answer 1

you will add the class .rcbScroll rcbWidth in head style tag to set the height attribute.

.rcbScroll .rcbWidth
{
height: auto !important;
}

Answer 2

Setting Height = "100%" fix my problem :)