Copy and paste of text with formatting causes style map reference error

[adrianmawer]

Version

1.6.6

Test Case

https://jsfiddle.net/adrianmawer/afftoutf/

Steps to reproduce

See screen cast: http://youtu.be/VgGit4W7Lyc

1. in a fabric.Textbox, highlight/select some text and apply some formatting e.g. underline.
2. highlight/select the formatted text, copy it then paste it at the end of the line.
3. highlight the text that was originally underlined in step 1, remove underline formatting and observe that the pasted text also has its underlining removed. This is unexpected. Only the highlighted text should have its underlining removed.

Expected Behavior

Only the highlighted/selected text gets new formatting applied in its character style mapping

Actual Behavior

The pasted text received the new formatting too because the underlying style map entries are copied by reference instead being cloned.