MMT scala shell broken

In MMT/43fec2b39fba the mmt/scala subshell is somehow broken:

    $ deploy/mmt
    ...
    scala
    user: 'scala'
    It may take a few seconds for the Scala prompt to appear.
    user: 'scala' finished

Nothing happens afterwards, no Scala REPL.

(This might be due to the update to scala-2.13.4, where a few Scala compiler/interpreter internals have changed.)