Paste Special > Keep Existing Reference Designators sometimes fails

Description

In some, not all, cases, copying a symbol and doing Paste Special... > Keep existing reference designators results in a ? reference.

Possibly related to #15319 (closed) ?

Steps to reproduce

Open this project: testpcb.zip
Open schematic and navigate to the hierarchical sheet.
Select both symbols, J8 and R1, and copy.
Do Paste Special... > Keep existing reference designators

Result: R1 is pasted with designator R1, but J8 is pasted with designator J?

KiCad Version

Application: KiCad Schematic Editor x86_64 on x86_64

Version: 7.0.8-7.0.8~ubuntu22.04.1, release build

Libraries:
	wxWidgets 3.2.1
	FreeType 2.11.1
	HarfBuzz 6.0.0
	FontConfig 2.13.1
	libcurl/7.81.0 OpenSSL/3.0.2 zlib/1.2.11 brotli/1.0.9 zstd/1.4.8 libidn2/2.3.2 libpsl/0.21.0 (+libidn2/2.3.2) libssh/0.9.6/openssl/zlib nghttp2/1.43.0 librtmp/2.3 OpenLDAP/2.5.16

Platform: Linux Mint 21.2, 64 bit, Little endian, wxGTK, cinnamon, x11

Build Info:
	Date: Sep 30 2023 13:54:18
	wxWidgets: 3.2.1 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.5.2
	Curl: 7.88.1
	ngspice: 38
	Compiler: GCC 11.4.0 with C++ ABI 1016

Build settings:
	KICAD_SPICE=ON