Hey Paul,
Thanks for your answer and a happy new year!
While what you suggested is exactly what I thought at first, too, for me the difference in color seems to be far too enormeous to be related to the played string. Especially with very small intervalls upwards, for example, where I would expect little to no difference to a "normal" legato note. Also, the "Orchestral Strings" are the only one where the difference in color is audible at all to me. I find no such effect whatsoever with the "Apassionata Strings", "Chamber Strings", "Solo Strings" or "Dimension Strings".
Now that I've listened to it again more closely it seams to be not a muted string sound, but rather some kind of low pass filter effect, maybe a sample-rate related or compression related issue to me. Would be great if you guys could check those samples again, for it would be a shame to not be able to work with those beautiful Orchestral Strings to their full potential.