Resizing the end of the sequence event only modifies the duration of the sequence event.
I suppose that it is the same reason for which the sound is stoped when we split or change the begining position of an audio event ?
Without being of a high priority, I think that it would be a good think to be corrected, because it is something rather incomprehensible from the point of view of the user, since this limit is not present in any other software.
It is so evident to do it that it appears to be something like a bug when it is not…