Different behavior of TComboBox in Windows and Linux

[VicFer]

Hi all,
Lazarus 1.4.0 on Windows XP SP3 and Slackware64 14.1

On a combobox with AutoComplete set to True I begin to write and the autocompletion works as expected.
Then I press Enter and click on the down arrow.
On Windows the item list shows with the selected item highlighted and visible, but on Linux neither the item is visible nor it is highlighted.
I attach an example, any suggestion is appreciated.

Many thanks