God kväll, Rawaz,
It should be taut. If your pins are about to give, your strop was made for wimps. Or you are pulling too hard. Either way, that will not give you a good result.
Serves you right to hand over your money to the Perfidious Albion.
Thäter Brushes just do not behave that way. And no, what your brush is doing is
not normal. I usually strangle mine after use. That works marvels.