Just a tip to everyone with packet lost problems with a fast ethernet mikrotik product (R433,R433AH and so on) and ECI switches and fiber converter products with gigabit ports, we found that if you plug a fast ethernet (on mk) to a giga port (on ECI) even if the ECI port is set to 100mbp/s they will not talk with other properly. We tried several mk products with no sucess. The only way we found to solve this is to plug a giga port mk product and use it to bridge the other fast ethernet mk product.
I know the next question would be why do i want to plug a 100 mbp/s to a giga port anyway? This specific operator only deliveries on giga port even if you buy 2 or 4 mbp/s of internet and to keep our costs down we we were using the RB433 plugged direct to the ECI port with no good results.