A bit more digging reveals Petro Australis didn't get approvals...

A bit more digging reveals Petro Australis didn't get approvals from Cupet in time
for the 40% of Block 9
I bet they are kicking themselves now.
This from Melbana in 2018


Melbana Energy Limited Directors' report 30 June 2018 3 -in right with respect to a 40% participating interest in Block 9 PSC however this was subject to Petro Australis receiving the necessary Cuban regulatory approvals (including pre-qualification) for this transfer. Petro Australis failed to achieve pre-qualification to enable a timely application to Cuban regulatory authorities for their acquisition of a 40% participating interest in the Block 9 PSC. As a result, Melbana has terminated its commercial arrangements with Petro Australis. On 4 December 2017 the Company announced it had reached a commercial settlement with Petro Australis to conclusively resolve its claim to a right to acquire a 40% participating interest in the Block 9 PSC. The commercial settlement involved Petro Australis relinquishing all claims to its back-in right to the Block 9 PSC in consideration for Melbana paying A$50,000 in cash and issuing 20.8 million Melbana shares to Petro Australis. As a result of the settlement there are no further obligations on either party and it is confirmed that Melbana holds an unencumbered 100% interest in Block 9 PSC.