How to select cell content in a grid

I'm trying to select some grid cell content with the mouse to copy it to the clipboard. But the selection is always cleared after releasing the mouse button.
I found the same behavior in the vaadin sampler "Basic Features" - http://demo.vaadin.com/sampler/#ui/grids-and-trees/grid/features.

Only in the "Column renderers" sample - http://demo.vaadin.com/sampler/#ui/grids-and-trees/grid/renderers - it works much better - at least for the name column. The name column based on a HtmlRenderer and I try a HtmlRenderer in my sample too - but without success. So I have not idea where the diffrent is.

Can anyone suggest how to do something like that ?