Bootstrap modal losing textboxvalue after postback

I have some strange behavior with a bootstrap modal, the modal contains a textbox and an asp:button

When I click the button and inspect the value of the textbox in VB code behind - results in an empty string

If I remove the first and last lines from the code below, I can successfully read the value in the textbox from code-behind

Here is the modal markup:

 <div class="modal inmodal" id="modalUpdateDialog" tabindex="-1" role="dialog" aria-hidden="true">
        <asp:UpdatePanel ID="udpUpdateDialog" runat="server" UpdateMode="Conditional">
                <div class="modal-dialog">
                    <div class="modal-content animated bounceInDown">
                        <div class="modal-header">
                            <button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">×</span><span class="sr-only">Close</span></button>
                            <h4 class="modal-title">Update File</h4>
                            <small class="font-bold">Please enter your new description</small>
                        <div class="modal-body form-horizontal" style="height: auto; overflow: auto;">
                            <div class="form-group">
                                <label class="col-sm-2 control-label">Description</label>
                                <div class="col-sm-10">
                                    <asp:TextBox ID="txtNewDescription" runat="server" CssClass="form-control" />
                                    <asp:HiddenField ID="hdnRowID" runat="server" />
                        <div class="modal-footer">
                            <asp:Button ID="btnUpdateFile" runat="server" Text="Update File" class="btn btn-primary" UseSubmitBehavior="false" />

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BrianFordAuthor Commented:
FYI, I get the same issue with or without the updatePanel
BrianFordAuthor Commented:
Problem solved..

It turned out to be an issue with the Inspinia admin theme we are using, in particular the inpinia.js and jquery.slimscroll.min.js

For now we removed these and everything works great, next step is to log an issue with Inspinia :)

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BrianFordAuthor Commented:
Only took me 2 days to find this :)
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