Grid isn't calculating row height correctly in some cases when RowSpan is used

[zlatanov]

• .NET Core Version: All
• Windows version: 11
• Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes

The following XAML:

<Grid Width="400" Background="Black">
    <Grid.ColumnDefinitions>
        <ColumnDefinition />
        <ColumnDefinition Width="100" />
        <ColumnDefinition Width="100" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <Border Grid.ColumnSpan="2"
            Height="100"
            Background="Green" />

    <Border Grid.RowSpan="2"
            Grid.Column="2"
            Height="200"
            Background="Aquamarine" />

    <Border Grid.Row="1"
            Height="100"
            Background="Orange" />

    <Border Grid.Row="1"
            Grid.Column="1"
            Height="100"
            Background="Red" />
</Grid>

should render two rows, each with height of 100 because each element has a height of 100, with exception of the one that spans 2 rows, which has a height of 200.

However, the result is the following:

The second row is exactly 1.5 times the height it should be.

Expected behavior:

If we insert the following:

<Border Grid.Column="1" Height="100" />

Then the grid is rendered as expected.

An interesting observation is that if we set explicit width for the first column, which in my example has 1* width, then the problem disappears.

[miloush]

Your expected bahavior is on smaller window. What is the behavior you expect on larger window? Everything in your grid has fixed height so if the grid is stretched to bigger size (to cover the window), I would think empty space is expected?

[zlatanov]

Your expected bahavior is on smaller window. What is the behavior you expect on larger window? Everything in your grid has fixed height so if the grid is stretched to bigger size (to cover the window), I would think empty space is expected?

Ignore the windows, their SizeToContent property is WidthAndHeight. Try the xaml in an empty UserControl, or set the Grid's vertical alignment to Top instead of Stretch.