Hello,
I have received an answer from the developer: saving an associative symbol label as a GDL object is not prohibited by AC, but it is strongly contraindicated because the result is unstable. Most important technical reason: labels receive some of the important information through GDL globals, which have wrong values in the saved Library Parts when placed as labels (their "original" values were hardcoded into the saved Library Part's GDL script). In the Classifications and Properties label's current implementation, this might not cause a problem, but other labels (or this label's later implementations) might show absolutely bad information after saved as a new label libpart.
The workaround here is: with associative labels, if you uncheck "Hide with associated element" in the Lable's Settings Dialog. So if you uncheck this, the new label will appear with the correct saved label.
I hope this explains the situation. Please let me know if you have any further questions!
Best regards,
Minh
Minh Nguyen
Technical Support Engineer
GRAPHISOFT