The Collaborative International Dictionary of English v.0.48:

Problematic \Prob`lem*at"ic\, Problematical \Prob`lem*at"ic*al\,
   a. [L. problematicus, Gr. ?: cf. F. probl['e]matique.]
   1. Having the nature of a problem; not shown in fact;
      questionable; uncertain; unsettled; doubtful; as, his
      theory is problematic because it fails to explain several
      facts. -- Prob`lem*at"ic*al*ly, adv.
      [1913 Webster]

            Diligent inquiries into remote and problematical
            guilt leave a gate wide open to . . . informers.
                                                  --Swift.
      [1913 Webster]

   2. Having characteristics which will create difficulties or
      undesirable consequences; -- of a proposed action; as, the
      proposed law is problematic because it will cause many
      people to lose their jobs.
      [PJC]

WordNet (r) 3.0 (2006):

problematic
    adj 1: open to doubt or debate; "If you ever get married, which
           seems to be extremely problematic" [syn: debatable,
           problematic, problematical]
    2: making great mental demands; hard to comprehend or solve or
       believe; "a baffling problem"; "I faced the knotty problem of
       what to have for breakfast"; "a problematic situation at
       home" [syn: baffling, elusive, knotty, problematic,
       problematical, tough]

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "problematic":
   a bit thick, a bit thin, absurd, ambiguous, arguable, at issue,
   baffling, bewildering, beyond belief, bothering, confounding,
   confusing, confutable, conjectural, contestable, controversial,
   controvertible, debatable, deniable, difficult, discomposing,
   disconcerting, dismaying, disputable, disputed, distracting,
   disturbing, doubtable, doubted, doubtful, dubious, dubitable,
   embarrassing, enigmatic, hairy, hard of belief, hard to believe,
   iffy, implausible, in dispute, in doubt, in dubio, in question,
   inconceivable, incredible, indecisive, intricate, mistakable, moot,
   mysterious, mystifying, not deserving belief, open, open to doubt,
   open to question, open to suspicion, passing belief, perplexing,
   perturbing, precarious, preposterous, problematical, puzzling,
   questionable, questioned, refutable, ridiculous, sensitive,
   speculative, staggering belief, suppositional, suspect, suspicious,
   tall, thick, thin, touchy, tricky, unbelievable, uncertain,
   unconvincing, undecided, unearthly, ungodly, unimaginable,
   unsettled, unthinkable, unworthy of belief, upsetting