I've set my waterfall to drop slowly, and in versions 975, 984, and now 985, when I resize the SparkSDR window, the waterfall goes to maximum rate (?).
Stopping and restarting the radio puts the waterfall back to the drop rate I have set.
IIRC, I have seen this behavior in Linux (975?) and can say for certain it is the same for all the referenced version in Windows.