Dear Bryan,
I wrote to him now. He posted under the name of Abhidhammika. My Pali is not good enough to figure out this form. Suan suggested that we have to consider this as a poetical form. 
Nina. 
Op 8 sep 2013, om 05:07 heeft Bryan Levman het volgende geschreven:

PTS does suggest viññāṇam is participial in the sense that it should be conceived more as "minding" than as "mind", but it doesn't suggest that the actual form is participial. The present participle of vijānāti is vijānanto and vijānaŋ in the active and viñāyamāna in the passive, so I don't see how this can be a participal. Do you know where I can find a copy of Suan Lu Zaw's post?