This mostly applies to situation where a patch (diff) content is copied from a terminal window. A typical diff generated via svn diff --git command is in form of:

Index: trunk/c.txt
===================================================================
diff --git a/trunk/c.txt b/trunk/c.txt
--- a/trunk/c.txt       (revision 237)
+++ b/trunk/c.txt       (working copy)
@@ -219,3 +219,4 @@
 aa
 aa
 aa
+new line

where in from and to lines a path part (e.g. a/trunk/c.txt) is separated from a revision part ((revision 237)) with a tab (\t) character. When copying from terminal, tab can get replaced by a series of spaces which fools Crucible into treating a revision part as an extension of a path component: