Using msys2/mingw32 to cross-compile open62541 with conan and MSYS2_ARG_CONV_EXCL

I'm trying to cross-compile open62541 with conan/cmake/msys2/mingw32 and this fails with a particular error relating to paths.
I've narrowed it down to this command, invoked by cmake/make as part of a custom_command to generate some files.

/C/.conan/1fbf05/1/bin/msys64/mingw32/bin/python3.10.exe C:/.conan/bd88a7/1/src/tools/generate_datatypes.py --selected-types=C:/.conan/bd88a7/1/src/tools/schema/datatypes_transport.txt --type-bsd=C:/.conan/bd88a7/1/src/tools/schema/Custom.Opc.Ua.Transport.bsd --import=TYPES#C:.conan/bd88a7/1/src/deps/ua-nodeset/Schema/Opc.Ua.Types.bsd --type-csv=C:/.conan/bd88a7/1/src/deps/ua-nodeset/Schema/NodeIds.csv --no-builtin --internal C:/.conan/bd88a7/1/build/Release/src_generated/open62541/transport
Traceback (most recent call last):
File "C:.conan\bd88a7\1\src\tools\generate_datatypes.py", line 95, in
parser.create_types()
File "C:/.conan\bd88a7\1\src\tools/nodeset_compiler/type_parser.py", line 384, in create_types
self.parse_types()
File "C:/.conan\bd88a7\1\src\tools/nodeset_compiler/type_parser.py", line 411, in parse_types
self.parseTypeDefinitions(outname_import, file_import)
File "C:/.conan\bd88a7\1\src\tools/nodeset_compiler/type_parser.py", line 304, in parseTypeDefinitions
xmlDoc = etree.iterparse(
File "C:/.conan/1fbf05/1/bin/msys64/mingw32/lib/python3.10/xml/etree/ElementTree.py", line 1272, in iterparse
next(it)
File "C:/.conan/1fbf05/1/bin/msys64/mingw32/lib/python3.10/xml/etree/ElementTree.py", line 1249, in iterator
source = open(source, "rb")
FileNotFoundError: [Errno 2] No such file or directory: 'C;.conan\bd88a7\1\src\deps\ua-nodeset\Schema\Opc.Ua.Types.bsd'

Disabling the path conversion altogether works:

MSYS2_ARG_CONV_EXCL=- /C/.conan/1fbf05/1/bin/msys64/mingw32/bin/python3.10.exe C:/.conan/bd88a7/1/src/tools/generate_datatypes.py --selected-types=C:/.conan/bd88a7/1/src/tools/schema/datatypes_transport.txt --type-bsd=C:/.conan/bd88a7/1/src/tools/schema/Custom.Opc.Ua.Transport.bsd --import=TYPES#C:/.conan/bd88a7/1/src/deps/ua-nodeset/Schema/Opc.Ua.Types.bsd --type-csv=C:/.conan/bd88a7/1/src/deps/ua-nodeset/Schema/NodeIds.csv --no-builtin --internal C:/.conan/bd88a7/1/build/Release/src_generated/open62541/transport

I updated the python-script with some additional logging to print the arguments.

['C:/.conan/bd88a7/1/src/tools/generate_datatypes.py', '--selected-types=C:/.conan/bd88a7/1/src/tools/schema/datatypes_transport.txt', '--type-bsd=C:/.conan/bd88a7/1/src/tools/schema/Custom.Opc.Ua.Transport.bsd', '--import=TYPES#C;.conan\bd88a7\1\src\deps\ua-nodeset\Schema\Opc.Ua.Types.bsd', '--type-csv=C:/.conan/bd88a7/1/src/deps/ua-nodeset/Schema/NodeIds.csv', '--no-builtin', '--internal', 'C:/.conan/bd88a7/1/build/Release/src_generated/open62541/transport']

The reason I'm asking here is that the issue is specifically with the path that is prefixed with TYPES#, the others are unaffected.
Can you help me understand why? Hopefully that'll point me in the right direction to solve this. Thanks!

Reproduce the shown generate_datatypes.py command with and without MSYS2_ARG_CONV_EXCL=-, then inspect how MSYS2 path conversion handles the --import=TYPES# argument. The relevant Python entry points are tools/generate_datatypes.py and tools/nodeset_compiler/type_parser.py; done means the import path remains usable without breaking the other arguments.