When I use the ColumnSpan property on a floating label, the label itself will grow to the number of columns, but the content of the label will always get the size of the column the floating label is int.
Below is the code I've used:
@page "/gridLayout"
<TelerikGridLayout>
<GridLayoutColumns>
<GridLayoutColumn Width="200"/>
<GridLayoutColumn Width="200"/>
<GridLayoutColumn Width="200"/>
<GridLayoutColumn Width="200"/>
</GridLayoutColumns>
<GridLayoutItems>
<GridLayoutItem Column="1"
Row="1"
ColumnSpan="3">
<TelerikTextBox Title="Filial" />
</GridLayoutItem>
<GridLayoutItem Column="1"
Row="2"
ColumnSpan="3">
<TelerikFloatingLabel Text="Pessoa">
<TelerikTextBox />
</TelerikFloatingLabel>
</GridLayoutItem>
</GridLayoutItems>
</TelerikGridLayout>
This is how it's rendered: