CTrader unwanted partial closing

Hi everyone hope someone can enlighten me.

Last night I modified a stoploss on an open position, by using the slider on the chart. I was in a long position, and modified the stop-loss down to create a bit more room/risk. When I did this cTrader decided to partially close a portion of trade. 

Ctrader has never done this before when I have modified stoplosses, And I am no where near the margin closeout, I just can't see a reason why it would be partially closing

Any information would be greatly appreciated