update with select subquery doesn't work with $parent.$current

OrientDB Version: 3.1.9

Java Version: openjdk-8

OS: DockerFile FROM orientdb:3.1.9 (Debian GNU/Linux 10)

Expected behavior

I expect that:

update morph set uLevel = (select uLevel from nvdb where stem = 'ossia' and simpleType = 'conj') where simpleType = 'C' and stem = 'ossia';

and

update morph set uLevel = (select uLevel from nvdb where stem = $parent.$current.stem and simpleType = 'conj') where simpleType = 'C' and stem = 'ossia';

produce the same result (since the where in the update fixes the stem to the same value).
At least, unless I misunderstood $parent.$current or something changed between versions and I missed it.

Actual behavior

update morph set uLevel = (select uLevel from nvdb where stem = 'ossia' and simpleType = 'conj') where simpleType = 'C' and stem = 'ossia';

updates 1 record and uLevel value is 2 (as expected)

update morph set uLevel = (select uLevel from nvdb where stem = $parent.$current.stem and simpleType = 'conj') where simpleType = 'C' and stem = 'ossia';

updates 1 record, but uLevel value is null

Steps to reproduce

Well, I hope the above is sufficient, but let me know

Start by reproducing the two UPDATE statements from the issue against OrientDB 3.1.9 using the documented Docker environment, then inspect the SQL update and subquery handling involved in $parent.$current resolution. Done means the correlated subquery produces the expected uLevel value rather than null, with regression coverage for the reported statements.