On the singular coordinate transformations of the Schwarzschild metric

It is noted that the coordinate transformations usually used to demonstrate the continuity of geodesics at the Schwarzschild horizon are of class $C^0$, while the standard causality theory requires that the metric tensor to be at least $C^1$. Then this singular metric tensor leads to the appearance of the fictitious delta-like source in the Einstein equations, which prevents quantum particles to enter a black hole horizon.