Hello, Mason,  

The provided custom theme is greatly appreciated. I was able to observe the undesired style:

However, I was able to replicate the issue with the Crystal theme in the Demo application as well:

I have logged it in our feedback portal by making this thread public on your behalf. You can track its progress, subscribe for status changes and add your comments on the following link - feedback item.

I have also updated your Telerik points.

Currently, the possible solution that I can suggest is to handle the CreateCompositeFilterDialog event and move the buttons: 

    Sub New()

        InitializeComponent()
        ThemeResolutionService.LoadPackageFile("..\..\Crystal.tssp")
        ThemeResolutionService.ApplicationThemeName = "Crystal"

        Me.RadGridView1.EnableFiltering = True
        AddHandler Me.RadGridView1.CreateCompositeFilterDialog, AddressOf RadGridView_CreateCompositeFilterDialog
    End Sub

    Private Sub RadGridView_CreateCompositeFilterDialog(sender As Object, e As UI.GridViewCreateCompositeFilterDialogEventArgs)
        Dim d As CompositeDataFilterForm = TryCast(e.Dialog, CompositeDataFilterForm)
        d.DataFilter.Height -= 20
        d.Controls("radButtonOK").Top -= 20
        d.Controls("radButtonCancel").Top -= 20
    End Sub

I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik

Hello, Mason ,

Could you please specify which is the exact theme that you are using since it is difficult to conclude from the provided screenshot. In case you are using a custom theme, it would be greatly appreciated if you can provide the .tssp file of the theme so we would be able to investigate further.

Another thing that we should clarify is whether you are running the application at 100% DPI scaling or higher.

Thank you in advance for your cooperation.

I am looking forward to your reply.

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik