Jenkins 2.510 introduced a regression where you can not add 2 build steps of the same type into a FreeStyle job.

Steps to reproduce

Start Jenkins 2.510 or higher (java -jar jenkins.war --httpListenAddress=127.0.0.1)
Go through the setup wizard and install the recommended plugin, sign up etc.
Create a new FreeStyle Job
Click "Add build step" and choose "Execute Shell"
in the builder command enter "echo hello"
Add another step by clicking click "Add build step" and choose "Execute Shell"

Expected Results

A new entry is available where you can add the shell script details.

Actual Results

clicking on "Execute Shell" in the dropdown has no effect

Workaround

Add the first Build Step then save, edit the config and add the next build step. (rinse and repeat for as many duplicate steps as you desire)