Why is Saint Paul considered gnostic? (by some) I read that these verses (over other texts that are clearly gnostic but not attributed as such) are considered gnostic:

ST. PAUL TO THE EPHESIANS - Third letter


  For our wrestling is not against flesh and blood; but against
  principalities and power, against the rulers of the world of this
  darkness


ST. PAUL TO THE CORINTHIANS (2, 6 - 8)


  Yet we do speak wisdom among those who are mature; a wisdom, however,
  not of this age nor of the rulers of this age, who are passing away;
  but we speak God's wisdom in a mystery, the hidden wisdom which God
  predestined before the ages to our glory;  the wisdom which none of
  the rulers of this age has understood; for if they had understood it
  they would not have crucified the Lord of glory;


My question: Why is Saint Paul considered gnostic?



Consider these various examples of people forwarding or confronting the idea:


The Gnostic Paul - Book by Elaine Pagels
Was the Apostle Paul a Gnostic?
The Gnostic Paul - Random Blog post
Paul the Gnostic Opponent of Peter Not an Apostle of Historic Christianity (PDF)
It seems as though many that assert the possibility are either looking at why the Gnostics believed that Paul was a member of such, as Pagels, they are not Christian, as Massey, or are either mysticism or on the periphery of accepted or mainstream Christianity.

Pseudo-Apocrypha like The Apocalypse of Paul  and other Gnostic documents from Nag Hammadi seem to sway non-conventional or liberal leaning theologies to consider the possibility of Pauls Gnosticism.  


  What Muhammad 'All discovered at Nag Hammadi is, apparently, a library of writings, almost all of them gnostic. Although they claim to offer secret teaching, many of these texts refer to the Scriptures of the Old Testament, and others to the letters of Paul and the New Testament gospels. Many of them include the same  dramatic personae as the New Testament--Jesus and his disciples. Yet the differences are striking.
  
  Orthodox Jews and Christians insist that a chasm separates humanity from Its creator: God is wholly other. But some of the gnostics who wrote these gospels contradict this: self-knowledge is knowledge of God; the self and the divine are identical.
  - Pagels


In the Tekton article you listed Pagel even declines to declare if Paul is or is not gnostic. 


  Was Paul actually a Gnostic? The idea is taken seriously by no one in NT scholarship today; even Elaine Pagels, the Gnostic-promoter premier, declines in her book The Gnostic Paul to say yea or nay to whether Paul was actually a Gnostic, instead concentrating on how the Gnostics interpreted Paul's letters.
  - Tekton Apologetics


I would struggle to take Freke &amp; Gandy, authors of 'The Jesus Mysteries: Was The Original Jesus A Pagan God?' as serious Christian theologians and would classify them more toward mysticism.  

As for the Apocalypse of Paul, Augustine considered it bunk.


  St. Augustine laughs at the folly of some who had forged an Apocalypse of Paul, full of fables, and pretending to contain the unutterable things which the apostle had heard. This is, I doubt not, our book.
  - (Aug. on John, Tract 98.)


The 'Nazirene'  seems to be in the fringe and misrepresents Origins "Gospel  of God" as support for Paul's 'mysteries, of God.  Origen in fact fought against the gnostic heresies.

Massey, I believe I could say is not a Christian because he believes it is a myth and our gospels as a product of Gnosticism.  


  It has been shown in previous lectures that the matter of our Canonical Gospels is, to a large extent, mythical, and that the Gnosis of Ancient Egypt was carried into other lands by the underground passage of the Mysteries, to emerge at last as the literalised legend of Historic Christianity.
  - Massey


So, as far as the scripture verses you listed above, personally I don't see a gnostic connection with the Ephesians verse.  The 1 Corinthians verse and others, if taken in context with all of Paul's writing and the totality of all of scripture, would not justify a gnostic connection either.  

The answer to your question would be then that the reason 'some' believe Paul was a Gnostic is due to using non-canonical writings, non credible resources, or taking Pauls words out of context.  When theologians such as Augustine, Tertullian, Origin, etc. discredit inferences of any Gnostic bent of the Apostle Paul I've yet to see credible commentary on the contrary.  If I read some commentary from credible, even critical sources I may alter my answer.