Why I can't use the copy-paste from external sources in the incident/chat thread?
Workspace, Thread Control Relationship Item
Oracle B2C Service, All versions
Oracle B2C Service is using a utility called Tidy to verify that HMTL code is compatible with the XHTML format as an XML document, an XHTML document must meet a stricter set of requirements than HTML documents do. The way we ensure that documents are XML-compliant is by running them through the utility Tidy, a de facto industry standard software tool that cleans up HTML and offers a conversion into XHTML.
If the copy is used on a page/document that is not meeting the XHTML requirements which means that it can't be converted to XML file, then the paste function will not work on incident or chat thread control.
As a workaround, you can copy only the text or paste as text (CTRL + SHIFT + V). The copy as text function works only on incident thread. It is not available in a chat.
As a permanent solution, if you want to copy the formatting, you must be sure that the source copied has an XHTML format.
Additional information can be found on Answer ID 2673: Modifications to the HTML source of documents.