What you were expecting to happen, and what actually happened?
I put 225000 gold into a guild task, and received an error message. I got thrown out of the guild menu to the world map, and saw that the 225000 was indeed deducted from my total. I also received 10 keys that was apparently the reward for completing the task.
Going back into the guild task screen I noticed that the task has not been completed. It is still indicating task 9/12. What is further remarkable is that the task is showing that the reward should be 6 event keys, but I am sure that I received 10 event keys in the mail. My estimate is that the task has been competed, probably even more then once, but that the display is wrong.