After successful delivery of 200'000 Metal, 100'000 Mineral and 50'000 Vespene to 3 of the 4 pirate leaders, there was a failure with the 4th delivery to dread pirate T-800 on his capital. The amount of Metal and Mineral delivered was correct, but Vespene was only 30'236 delivered, although I sent 50'000... - Nevertheless, after that I sent the missing 20'000 Vespene, but after the arrival at his capital it was not cleared and still remain as "not fulfilled" on my Quest-List.

So, what happened? - Do I have to throwaway/deal out the whole bunch of Metal, Mineral and Vespene again? - If this would be the case; may I be glad about a refund/reimbursement of my lost goods?!

This is addressed to the admins, kind regards.

yes you will have to resend all metal mineral and gas in one go!
as for why it did not send the right gas only admin can say but i would assume it was used for the flight? 

@enahs: Thanks for your reply. - To your assumption, that the gas was used for the flight; but why only in this flight? With the other 3 it worked properly, the payload was the same...

As per logs you sent Metal 200000, Minerals 100000, Vespene 30236. To fullfil the Quest you have to send Metal 200000, Minerals 100000, Vespene 50000 in one fleet.
It is not a bug.