Prefixmappings are not removed permanently from graph with DELETE

Prefixmappings are not removed permanently from graphs with DELETE. When adding triples to a graph that was deleted earlier old prefixmappings appear unexpectedly.

EXAMPLE:

PUT http://localhost:3030/example/data?graph=http://example.org/foo#
@prefix foo: <http://example.org/foo#> .
foo:foo foo:foo foo:foo

DELETE http://localhost:3030/example/data?graph=http://example.org/foo#

PUT http://localhost:3030/example/data?graph=http://example.org/foo#
@prefix bar: <http://example.org/bar#> .
bar:bar bar:bar bar:bar .

GET http://localhost:3030/example/data?graph=http://example.org/foo#

This returns both old and new prefixmappings:

@prefix bar: <http://example.org/bar#> .
@prefix foo: <http://example.org/foo#> .
bar:bar bar:bar bar:bar .