Hello Jaime,
If you need a fast turnaround and response, I advise that you open a support ticket. This is a public forum and we do try to monitor and help, yet we cannot guarantee (timely) responses.
Now, to get back to your actual question - I advise that you start troubleshooting this by following this article: http://docs.telerik.com/devtools/aspnet-ajax/general-information/troubleshooting/skins-troubleshooting#incorrect-or-distorted-appearance.
My best guess is that there are other controls with a different render mode (e.g., a menu or context menu) that bring unexpected styles to the page.
My second guess is that this happens only in IE when it is in Compatibility Mode and so you must move to Standards (Edge) mode.
If this does not help, could you modify this sample so it showcases the issue:
<telerik:RadGrid RenderMode="Classic" AutoGenerateColumns="false" ID="RadGrid1" DataSourceID="SqlDataSource1"
AllowFilteringByColumn="True" AllowSorting="True" Width="100%"
ShowFooter="True" AllowPaging="True" runat="server">
<GroupingSettings CaseSensitive="false"></GroupingSettings>
<MasterTableView AutoGenerateColumns="false" AllowFilteringByColumn="True" ShowFooter="True">
<Columns>
<telerik:GridMaskedColumn DataField="OrderID" HeaderText="OrderID"
FilterControlWidth="50px" AutoPostBackOnFilter="false" CurrentFilterFunction="EqualTo"
FilterDelay="2000" ShowFilterIcon="false" Mask="#####">
</telerik:GridMaskedColumn>
<telerik:GridBoundColumn FilterControlWidth="120px" DataField="ShipName" HeaderText="ShipName"
AutoPostBackOnFilter="true" CurrentFilterFunction="Contains"
ShowFilterIcon="false">
</telerik:GridBoundColumn>
<telerik:GridDateTimeColumn DataField="OrderDate" HeaderText="OrderDate" FilterControlWidth="110px"
SortExpression="OrderDate" PickerType="DatePicker" EnableTimeIndependentFiltering="true"
DataFormatString="{0:MM/dd/yyyy}">
</telerik:GridDateTimeColumn>
<telerik:GridDateTimeColumn FilterControlWidth="95px" DataField="ShippedDate" HeaderText="ShippedDate"
PickerType="DatePicker" EnableRangeFiltering="true">
<HeaderStyle Width="160px"></HeaderStyle>
</telerik:GridDateTimeColumn>
<telerik:GridTemplateColumn FilterControlWidth="80px" DataField="ShipCountry" HeaderText="ShipCountry">
<ItemTemplate>
<img src='Img/<%# Eval("ShipCountry") %>.gif' alt="" style="vertical-align: middle; margin-right: 7px;" /><%# Eval("ShipCountry") %>
</ItemTemplate>
</telerik:GridTemplateColumn>
<telerik:GridBoundColumn FilterControlWidth="50px" DataField="ShipPostalCode" HeaderText="ShipPostalCode">
<FooterStyle Font-Bold="true"></FooterStyle>
</telerik:GridBoundColumn>
<telerik:GridNumericColumn HeaderStyle-Width="130px" FilterControlWidth="50px" DataField="Freight"
DataType="System.Decimal" HeaderText="Freight" Aggregate="Sum" DataFormatString="{0} kg">
<FooterStyle Font-Bold="true"></FooterStyle>
</telerik:GridNumericColumn>
</Columns>
</MasterTableView>
</telerik:RadGrid>
<asp:SqlDataSource ID="SqlDataSource1" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
ProviderName="System.Data.SqlClient" SelectCommand="SELECT * FROM Orders" runat="server"></asp:SqlDataSource>
Regards,
Marin Bratanov
Progress Telerik