It is because "brave" has made a maximum bid higher than you are making (e.g. 1000 silver).
It does not show "brave"s maximum bid, because he do not need to make it to have the highest bid (e.g. a third account have made a bid om 600 silver and thereby forcing "brave" to bid 601 to still have the highest bid, this is done automatic when the third account makes the bid of 600 silver without "brave" needs to do anything).
When you then bid 603 silver, "brave"s bid changes to 604 (it is still below "brave"s maximum bid)
This continues until somebody bids more than "brave"s maximum bid or the auction ends.
I hope my explanation is understandable, otherwise I can try again
PS. There might be some special cases/rules that prevent pushing of silver between accounts.