Hi Mark,
For Adding NumberFormatInfo to UpDown control we should use System.Globlization.NumberFormatInfo class. Here I have created the sample which is contain Numeric UpDown with XAML level NumberFormatInfo and it's working fine. I couldn’t reproduce your issue.
Here is the code :
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sync="clr-namespace:Syncfusion.Windows.Tools.Controls;assembly=Syncfusion.Tools.WPF"
xmlns:shared="clr-namespace:Syncfusion.Windows.Shared;assembly=Syncfusion.Shared.WPF"
xmlns:sg="clr-namespace:System.Globalization;assembly=mscorlib"
Title="Window1" Height="300" Width="300">
Name="ctlUpDown" Height="25"
Margin="0"
BorderThickness="1"
BorderBrush="Gray">
Please let me know if you have any question.
Thanks,
Asem Ibohal Meitei.