@ Tausendberg I replicated your initial issue, standalone, Mac.
For me however, the second held chord continued to s&h until the first note of the first chord was released ie adding the second chord did not stop the s&h; it was releasing the first note/chord that stopped the s&h. This leads me to think it's something to do with the triggering of the s&h function commencing and ending with the first key played.
It does this with 'legato' selected or not, playing in legato fashion in polyphonic 16 voice mode, no matter what trigger source is selected (external or internal). It feels like it picks one key only to determine when to generate the effect.
e.g. play a two handed arpeggio'd chord, starting from the lowest note, hold the chord, then release the lowest note. The s&h stops for the remaining held notes.
The issue might be classified as 's&h stops when the first key is released'
[UPDATE] using template patch 'S and hold', poly, 3 voices, try playing a 4 note chord. It appears the 'culprit' note is not always just the first key played, it's the first voice assigned (after all voices have been used, or all freed up).