Alfresco 4.2 (Enterprise and Community) has a problem editing comments on Internet Explorer 8, 9 and 10. This issue occurs when external content is pasted on the comment box: all the text entered previously by the user is deleted.
More information can be found at:
This issue will be fixed on version 4.3.
To solve this problem in Alfresco 4.2, simply overwrite (either by extension or by module AMP) the comments component with source files from version 4.1: