Atlassian Editor auto escapes copy pasted special characters even in code blocks - (ED-1158)

Atlassian Editor escapes any copy pasted content even if it is in a code block. For example

#!
~~~~
[test]

~~~~

would result in

#!
\[test\]

Workaround

Open the code block (with ``` or by clicking the button), then paste the contents into the code block.