A number of Chinese characters are simplified-traditional multipairings (简繁一对多; 簡繁一對多), which do not have a one-to-one mapping between their simplified and traditional forms.
[1] This is usually because the simplification process merged two or more distinct characters into one.
[2] In most cases, these traditional characters are homonyms, having the same pronunciation but different meanings.
As a result, converting text from simplified to traditional characters is difficult to automate, especially in the case of common characters such as 后⇄后後 (behind, empress), 表⇄表錶 (table, clock), 奸⇄奸姦 (traitor, rape) and more.
The following is an exhaustive list of all characters whose simplified and traditional forms do not map in a one-to-one manner.