After starting the fluorescent lamp the starter still glows on but does not close circuit, is that normal or is there something wrong. Here you can see what i mean: https://www.youtube.com/watch?v=vlfyaPTq2ao

Low triggering voltage of the neon-argon gas filling in the glow bottle, which is enough to continue to make it glow, even after the lamp has fired up, and limits the voltage to the starter.

Strange thing is that it only afterglows in a long 150cm 58/65W fixture, i also tryed on 120cm 36/40W and there is no afterglow. I am affraid that the afterglow will worn out the starter and lamp earlier because there is a slight connection through the starter

It is the main lamp reignition overshoot, what causes some time when there is enough voltage for the glow discharge to happen.
As the main lamp gets older, the overshoots get larger and the glow in the starter more intense. At some point the glow is so intense the starter contacts do close and the well known EOL flashing show starts. That is the normal life cycle of the starter/lamp combo, because it accelerates over time, most of the changes happen few 100's hours before EOL.
But even before the contacts close, the long term heat from the discharge degrades practically all parts of the starter, so therefore it should always be replaced with the lamp at EOL - otherwise it will very likely damage the new lamp.
The "protected" starters could be life rated for three lamps, because the thermal cutout trips and disables the starter when only limited damage is done, so when the lamp is really replaced once the cutout trips, it may be kept in service over multiple lamps (most makers rate it for 3 lamps).

It is the main lamp reignition overshoot, what causes some time when there is enough voltage for the glow discharge to happen.
As the main lamp gets older, the overshoots get larger and the glow in the starter more intense. At some point the glow is so intense the starter contacts do close and the well known EOL flashing show starts. That is the normal life cycle of the starter/lamp combo, because it accelerates over time, most of the changes happen few 100's hours before EOL.
But even before the contacts close, the long term heat from the discharge degrades practically all parts of the starter, so therefore it should always be replaced with the lamp at EOL - otherwise it will very likely damage the new lamp.
The "protected" starters could be life rated for three lamps, because the thermal cutout trips and disables the starter when only limited damage is done, so when the lamp is really replaced once the cutout trips, it may be kept in service over multiple lamps (most makers rate it for 3 lamps).

A very good explanation, thank you.

When starter glows dimly after preheating the lamp that means that breaking voltage of starters gas is low.It is caused by passing little current through glow bottle.