Fill series, date, weekdays, starting value = 2, step value = 1.5

I play with Excel to learn its "philosophy". I made date series across weekdays with step values 1 and 1.5 and across days with step value 1.5 There was an abnormality in weekday series with the step value 1.5 First it looks fine, as it takes 20.5 as 20 and 23.5 as 23, however after skipping 25 (because it is weekend), it takes 26.5 as 27 and so on and even skips 4 and 7, although they are not weekends. Why is it like that? How does Excel think in this case?
I know in practice step value equal to 1.5 will not be needed in date series, but I just want to know how Excel thinks.
Thanks for your help beforehand.question_excel.png

What is the formula in column F? Suggest you increase the format to date and time to maybe get a better understanding of how Excel treats the half day increment.