looks like it has something to do with the screen resolution of the second screen.
Now I tried another older IBM screen also with 1280x1024 max resolution and got the same issue, only larger screens seem to work...
[ 7426.139] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.405] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.678] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.953] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.208] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.476] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.742] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7428.024] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7428.301] (II) intel(0): resizing framebuffer to 1600x900
[ 7428.301] (II) intel(0): switch to mode 1600x900@60.0 on LVDS1 using pipe 0, position (0, 0), rotation normal, reflection none
looks like it has something to do with the screen resolution of the second screen.
Now I tried another older IBM screen also with 1280x1024 max resolution and got the same issue, only larger screens seem to work...
[ 7426.139] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.405] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.678] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7426.953] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.208] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.476] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7427.742] (II) intel(0): switch to mode 1280x1024@76.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7428.024] (II) intel(0): switch to mode 1280x1024@60.0 on VGA1 using pipe 1, position (1600, 0), rotation normal, reflection none
[ 7428.301] (II) intel(0): resizing framebuffer to 1600x900
[ 7428.301] (II) intel(0): switch to mode 1600x900@60.0 on LVDS1 using pipe 0, position (0, 0), rotation normal, reflection none