嵌套在TabControl中的Syncfusion GridDataControl：切换选项卡后自动调整大小的列

I am rather new to WPF. On .NET 3.5 using C# I want to build a WPF application including Syncfusion's GridDataControl in a TabItem. The GridDataControl is supposed to auto-resize by specifying the column width in multiples of '*'. This works fine after the first start of the app. But after switching tabs and again switching back resizing is broken and the grid control remains fixed in size. Here is my xaml code:I am rather new to WPF. On .NET 3.5 using C# I