Problem with CSS linear-gradient

Hi all,
I try to overwrite the background image (linear-gradient) of selected cells in a grid:

.v-grid-row-selected > .v-grid-cell {
  background-image: linear-gradient(black 33.3%, red 33.3%, red 66.6%, gold 66.6%);
}

But the compiled CSS I see is

background-image: linear, black 33.3%, red 33.3%, red 66.6%, gold 66.6%;

This is not valid and so the background image from original theme is used.
Any ideas? Maybe it's a bug?
Vaadin 7.6.3
Thanks in advance
Maik
 

Google is your friend... -> www.google.de/search?q=vaadin+sass+linear-gradient -> vaadin.com/forum#!/thread/8127922

took me about ten seconds to find it...