current_timestamp variable being replaced in create table statement

table definition is being altered by server:
create a simple table:

CREATE TABLE t1 (

  ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP

);

...this is being returned by the server to read:

CREATE TABLE t1 (

  ts timestamp DEFAULT current_timestamp() ON UPDATE current_timestamp()

);

The brackets appearing after the variable CURRENT_TIMESTAMP are being added (presumably replacing the variable with the function), which causes problems with unexpected changes in the DDL.

This does not happen in 10.0.24.
I do not know whether it happens in 10.1.x