Benjamin: I thank you too for verifying that I was not crazy.

Martin: I noticed native/non-native split too, and chalked it up to a
subtle difference between German and English.

For future reference, the problem with the original, as I see it now, is
a subtle interaction between syntax and semantics.  The original
sentence combined two thoughts about has_key.  The two should be either
coordinate (parallel in form) or one should be clearly subordinate.  A
subordinate modifier should generally be closer to the subject,
especially if it is much shorter.  Making that so was one of my
suggestions.  The coordinate form would be 'but it is deprecated'.  But
this does not work because 'it' would be somewhat ambiguous because of
the particular first modifier.  

The following pair of sentences illustrate what I am trying to say.
  Guido was once a Nederlander, but he moved to America.
  Guido was once a student of Professor X, but he moved to America.
In English, the second 'he' is ambiguous because of the particular first
modifier.

So, to me, 'but deprecated' at the end of the sentence reads as either a
misplaced subordinate form or as an abbreviated coordinate form that is
at least somewhat ambiguous because of the meaning of the other modifier.