capabilities: THREAD=REFERENCES
state: created

ok append
ok append
ok append
ok append

ok select $mailbox
ok thread references us-ascii all
* THREAD (1 2 3 4)

ok store 1,2 +flags \deleted
ok expunge
ok thread references us-ascii all
* THREAD (1 2)

ok append
ok thread references us-ascii all
* THREAD (1 2 3)