When I solve the circuit, using superposition, I get there is a current flowing thorough the ideal voltage source in the right. What will the voltage source in the right actually do? Will it become like a resistor and cause to a voltage drop of 4v?
You need to define a reference point, I've put it below the 50V source. The 4V source does not actually behave like a resistor, it doesn't influence the current due to its internal resistance but rather just 'reduces' the overall applied voltage (what of course also influences the current). Due to this, the resulting current flowing from the positive of the 50V to the negative is
No, it's not a resistor. It's a creature that current flows in it independently of its own voltage. The voltage is just given, and current flows, so all the mesh behaves according to Kirchhoff's law.
Imagine a battery. A stronger battery can still push electrons towards it, that doesn't change the voltage of the battery itself.