When line in "Properties Content" ends with backslash, newline is escaped and the property on the next line doesn't exist, because it's part of the line ended by backlash.
Environment:
Jenkins 1.447.2 @ Tomcat 7.0.28 and Java 1.6_33
EnvInject 1.60
Windows 2003 (32bit)
There is a conflict with multiple line keys.