I'm having similar problems as well with the step duration: see this
https://youtu.be/8dTlwkcE0mA (unlisted)
In that example scene, originally all steps were created with the shortcut CTRL+"+"; they were initially set to last 00:00:30 each, after a couple of run with no issues I changed the step duration to two seconds only in "Red2".
The change in duration appeared to affect the "white" step.
Earlier today I noticed similar issue also while programming other scenes with blinders, in some cases certain steps were even skipped.
I'm using Windows 10 and SweetLight 64 bits.