Can be found by doing multiple buy or sell orders of the same block type to a trade node.
The 1st time you do it, the price you're buying is the actual price and you don't notice an issue.
The 2nd time, the price didn't update in the UI but it did in reality. So you end up with a price that's higher or lower than what you're shown.
Because of that, the trade order menu shows you the wrong credits but completing the order will use the correct amount of credits (or the shop will complain you don't have enough credits).
Restarting the server updated the prices again for me.