Worldmap line visible only when Cluster mouse over

Hi,

Almost all explanations are in the topic title.

I want to draw some lines on the worldmap even if I see the associated layer in the list.
In addition, when the desired lines are betwenn markers and markers are clustered due to zoom, the lines are visible when the mouse passes over hte cluster number. But if I zoom in, no line at all.

Did somebody already see this behavior?