GParted doesn't see Debian Live partition?

[Markus Laire <malaire@gmail.com>]

I just put debian-live-9.0.1-amd64-xfce.iso to 128 GB USB-stick and
then tried to check the created partitions on a computer running
Debian Strech.

When I check partitions with "cat /proc/partitions" I get:
   8       48  123240448 sdd
   8       49    1896832 sdd1
   8       50        416 sdd2

So there is one main partition and one tiny one.

But if I start GParted to modify partitions, it doesn't see main
partition at all, only the tiny one. GParted claims that USB-stick
has:
- 1.04 MiB unallocated space
- 416 KiB fat16 partition
- 117.53 GiB unallocated space

Why GParted doesn't see the main partition? I want to create another
partition for persistence, but I'm afraid GParted will destroy main
partition (which it doesn't see) if I try to do any changes.

-- 
Markus Laire
https://www.MarkusLaire.com