That is now my concern too . Yesterday I noticed a number of times that my upvoting caused a decrease in SBD to some peoples posts. As akrid is mentioning it was maybe a coincidence that the price of SBD dropped at the time I was making these upvotes.
I just have expressed my concerns and I will monitor this thoroughly during the next period of time. I will remain bringing this up if it happens again.
Thanks for your reply.