BUT after mining a bit,
it starts to increase, decrease, etc, as if you don't put anything!
I haven't tested explicitely, but some (most?) pools will force a variable diff if you mine too fast or too slow with a fixed diff. Look at the log, if you get a message "Pool changes Difficulty to XXXX." so that's your pool's job, JCE don't change the diff by itself. I'll switch one rig to that pool for a few hours to check for that (but I mine v7 and not Heavy since i've low-mem cards).
Hi again and thanks for the answer.
So, i do get the message: "Pool changes Difficulty to XXXX." therefore as you say it's a pool's job.
Weird part is that when using fixed diff like 25k with jce-miner, diff changes after some time but same 25k with xmr-stak, diff stays fixed... :/
Cheers!