Gary, I cannot replicate that inconsistency in 3.9.0.


>>> x = "abc"
>>> x is "abc"
<stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?
True
>>> if x is "abc": pass
... 
<stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?


I don't believe that you should be getting a SyntaxError at all, and both cases should give the same warning. Can you double-check your code, and if you confirm that they give a different result or a SyntaxError, let us know here. Otherwise Raymond and Dennis are correct: this is working correctly.