What is wrong with foreign key constraint checks on column tables?

Here is a problem I've faced in the past:

SET SCHEMA DEV_DKH98X8NRPP3883BMMRIRSW8N;

--Create test data

CREATE COLUMN TABLE A(ACOL1 INT, ACOL2 NVARCHAR(10));

ALTER TABLE A ADD CONSTRAINT PK_A PRIMARY KEY (ACOL1);

INSERT INTO A(ACOL1, ACOL2) VALUES(1, 'One');

INSERT INTO A(ACOL1, ACOL2) VALUES(2, 'Two');

CREATE COLUMN TABLE B(BCOL1 INT, BREF1 INT, BCOL2 NVARCHAR(10));

ALTER TABLE B ADD CONSTRAINT FK_A_B FOREIGN KEY (BREF1) REFERENCES A(ACOL1);

INSERT INTO B(BCOL1, BREF1, BCOL2) VALUES (10, 1, 'Ref to 1');

INSERT INTO B(BCOL1, BREF1, BCOL2) VALUES (11, 2, 'Ref to 2');

--Check join

SELECT ACOL1, BCOL2

FROM A

JOIN B ON A.ACOL1 = B.BREF1

--Damage the foreign key

ALTER TABLE B ALTER (BREF1 INT NOT NULL); -- why it is permitted?

--Try to remove the foreign key now

ALTER TABLE B DROP CONSTRAINT FK_A_B;

--ERROR:

--Could not execute 'ALTER TABLE B DROP CONSTRAINT FK_A_B' in 48 ms 917 µs .

--SAP DBTech JDBC: [397] (at 30): invalid object name: invalid constraint name: line 1 col 31 (at pos 30)

--Check if the foreign key still exists

SELECT TOP 1 * FROM REFERENTIAL_CONSTRAINTS WHERE CONSTRAINT_NAME = 'FK_A_B';

--Yes it is still there

--DEV_DKH98X8NRPP3883BMMRIRSW8N;B;BREF1;1;FK_A_B;DEV_DKH98X8NRPP3883BMMRIRSW8N;A;ACOL1;PK_A;RESTRICT;RESTRICT

--Clean up (will delete damaged constraint)

DROP TABLE B;

DROP TABLE A;

So, the questions are:

1) Why changes to colums of foreign key references are permitted on column talbes? I think this is a bug, because the problem will not reproduce on row tables.

2) Is there any other way to get rid of damaged constraints instead of dropping the table?