These are the printless long legs, the other long legs don't have this problem,
just the printless ones
Hi and welcome
Please, post Studio and/or PartDesigner issuers on their dedicated forum: https://forum.bricklink.com/
(menu Studio » Resources » Studio Forum).
And please give more information.
What are you trying to do and what are you exactly doing?
AFAICT, plain long legs aren’t in Studio and even the decorated ones aren’t directly
accessible in PartDesigner.