Hello everybody. Faced with such a problem. From version 2.4.4.x, spacecraft became "difficult" to take off.
When testing 5 m of a normal tank and 1.25 m -> 5 m of a scaled tank, I saw a difference in the value of "Ballistic coefficient".
The formula is significantly affected by the diameter, as the shapes of the tanks as a result are the same and the coefficient and can be neglected.
Normal tank: C = 712 kg / m2
Scalable tank: C = 7019 kg / m2
If we take as a standard a normal tank, the diameter for the formula will be approximately as follows:
Normal tank: d = 5 m
Scalable tank: d ~ 8 m
This strongly affects the air resistance and in the career of the spacecraft that flew on the moon, now can not get into the orbit of Kerbin. Rolled back to version 2.4.3.21.