Hafidh al-Iraqi said in “Sharhul alfiyatul hadeeth”: As for not the fabrications, then it is permitted to show softness in the chains, and transmitting, without announcing their weakness. If that is not about al-Ahkam or Beliefs, but about Targheeb and Tarheeb in speeches, stories, merits of deeds and others like these. But if (ahadeeth) are about al-Ahkams of Sharia from halal and haram, or about beliefs, like Sifaat of Allah Taala, then it is not permitted to show softness (in accepting chains of such). And from scholars which seen that it is permitted to show softness (regarding weak chains of ahadeth in Targheeb and Tarheeb and etc), and show proofs for that from Imams: Abdurrahman ibn Mahdi, Ahmad ibn Hanbal, Abdullah ibn Mubarak and others. (Quoted from Ajwibatul Fadeela of imam Lucknawi p 39-40)
gift2shias.com 
Salaam.
Imaam Muslim’s position is that the defect should be announced or else the unauthentic hadeeth should not be quoted at all, regardless of which topic it deals with even targheeb and tarheeb as it is equally a part of the Share’ah and consequently needs authentic proof.
See: Introduction to Saheeh Muslim, and Introduction to Saheeh-ut-Targheeb wat-Tarheeb.
Jazaakallaahu khairan.