Hi Joubarbe.
I don't have Mint 17.2 to test it, but on 17.1 it depends on the choosed theme:
With 'Mint-X-????' on the controls, there's only a small spaces between the buttons,
with e.g. 'Adwaita'-theme the line appears in the toolbar.
There's API-command ...
gtk_separator_tool_item_set_draw (GtkSeparatorToolItem *item, gboolean draw)
which switches between a line or space.
And here's the real problem. There's no simple way to get the *item (widget-adress of toolbar-element) from PureBasic to switch to the 'line'-mode. The better way would be, that PB-commands like ToolBarSeparator() with a empty 'Return', would return the widget-adress to get API-access to toolbar-elements.
Regards, Charly