Postgres 12: backend crashes when creating non-deterministic collation

I was trying to learn how the new non-deterministic collations in v12 work, but the following makes the backend crash:

CREATE COLLATION de_ci (provider = icu, locale = 'de-x-icu', deterministic = false);

Which leads to:

2019-10-04 11:54:23 CEST LOG: server process (PID 7540) was terminated by exception 0xC0000005
2019-10-04 11:54:23 CEST DETAIL: Failed process was running:
CREATE COLLATION de_ci (provider = icu, locale = 'de-x-icu', deterministic = false)
2019-10-04 11:54:23 CEST HINT: See C include file "ntstatus.h" for a description of the hexadecimal value.
2019-10-04 11:54:23 CEST LOG: terminating any other active server processes
2019-10-04 11:54:23 CEST WARNING: terminating connection because of crash of another server process
2019-10-04 11:54:23 CEST DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.

This is on Windows 10 with the Postgres 12 binaries from EDB.
Exact Postgres version is: PostgreSQL 12.0, compiled by Visual C++ build 1914, 64-bit
The database was pg_upgraded if that makes any difference

I might have misunderstood how to use deterministic to create a case-insensitive collation, but I don't think the backend should crash if I do something wrong ;)

Regards
Thomas