when_string and when and errors going from ansible 1.1 to 1.2

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1

Hi,
I had some conditional tasks like this:

when_string: ${inventory_hostname} not in ${result.list_vms}

They worked in 1.1
In 1.2 they aborted with:

fatal: [127.0.0.1] => Conditional expression must evaluate to True or
False: ... "

After some noodling around I figure out that I needed to change it to:

when: inventory_hostname not in result.list_vms

and it worked.

So my questions:
1. is this expected?
2. is when_string completely deprecated?
3. if so then maybe a nicer error is in order?
4. if not then what is wrong in the first example?

Thanks,
-sv