Dear Valued Client,
Effective immediately our minimum Deal Size for foreign currency trading has increased from 1 (designated as 0.0001 on the MBT Navigator) to 1000 (designated as 0.1 on the MBT Navigator). Please note that any attempt to place an order with a size less than 1000 (0.1 on the MBT Navigator) will be rejected.
If you require assistance in closing a position of less than 1000 please do not hesitate to contact us at toll free 866-628-3003.
We apologize for any inconvenience,
MB Trading Futures
From another source:
We have also increased the minimum amount you are able to trade in the FIX live environment for FOREX to 1 micro lot for the time being for
So it is happening for performance reasons... could be that some automatic trading systems put too much pressure on the servers with many tiny orders.
The phrase "for the time being" means, that maybe they change this policy at some time in the future... we will see.