Encrypting twice with same key gives back plain text I read in the answer here that when encrypting twice the plain text with same key could result in plain text as shown below

$encrypt_{key}((encrypt_{key}(plain)) = plain $

Which block-cipher algorithms are they? What is this property called in general? Is it considered weak?

Edit 1 : the question is about block ciphers, not block cipher modes of operation
Edit 2 : added more clarity to the question through an equation
These block ciphers are called involutional ciphers, after the (mathematical) involution property of a function. This article shows a cryptographic analysis of two of them: Khazad and Anubis.

Neither Khazad nor Anubis  seem to be broken at the time of writing, basically they use the same internal structure for normal block ciphers, replacing the inner components with involutional ones.