Sorry Fangk, best to get advice from your accountant.
But I would have thought this was not short selling.
It is just trading in and out of shares within 12 months, and then buying in again - so no capital gains discount available to you for the initial sell transaction. Basically you would pay tax on the profit of the initial transactions (A and B), and C would be just a separate buy transaction.
If you buy a parcel of shares and then another equal parcel of shares and subsequently sell one of those parcels then you do have the option of deciding which of the two parcels you bought would be counted against the sale when determining profits/losses. To do this you must properly record your transactions for each parcel. Most people use a FIFO (first in, first out) approach to their transactions on shares, and if you deviate from that then must keep good records.
loki (hope this helps)
GRY Price at posting:
16.5¢ Sentiment: None Disclosure: Held