Hello guys,
I am here as well

So what happens is a lender borrowing up to his tradable balance (which was high enough to let him borrow all the orderbook or so), and paying interests due (or maybe it will be his evening surprise

). In other words, playing by the rules.
Now from my point of view it was not profitable for him to do this, but as long as users are playing by the rules there is nothing we can do. After all if someone want to borrow as much as he can to spike the rates regardless of his costs, then there is nothing we should do from a free market perspective. Similarly if people want to go long at more than 0.1% per day, there is nothing we can do either...
With that said, all ideas are welcome to ensure that unused swaps are not used for manipulation. We could double charge the closing of unused swaps without using them (but it would penalize legitimate use as well). We could prevent closing unused swaps manually (ie you can only use your swaps in a margin position or let it expires until the end of its period). What else?
Or we can just wait for people to realize costs/benefits of manipulation has become too high.
Anyway thank you for your analysis and have a good day
Raphael