IconTransformation works improperly cross Syntax

In class IconTransformation, I detected that it always use

@Requirement("plain/1.0")
private Parser plainTextParser;

to parse a given configuration source into an XDOM which is used to map with the input XDOM later. It means we always compare a static one with a dynamic one(based on its syntax: XWiki, Confluence, TWiki,...).
So my proposal is to look up the parser dynamically by rendering context.(Patch for 2.7.1 is attached to explain further)