Steps to reproduce:
======================================================
1) create a file in project (i. e. "A.java")with just one symbol: "A" and left a
new line at the end of the file. the file will look like this:
--------beginning of the file----------
A

--------end of the file----------------
2) create a file named patch.diff with this content:
--------beginning of the file----------
1c1
< A
---
> B
--------end of the file----------------
3) in the project tree view right click on the file and select "Tools" -> "Apply
Diff Patch"
4) select file patch.diff that you've created in previous steps
5) select "No"
6) the patch will change symbol "A" to symbol "B" in the source file
Problem: the "Undo function" isn't available to undo patching.