High-Speed electronics - Reflections in T-intersection
However, we now got a question to explain why we get reflections in a
  "T-intersection" even though we match the load resistance with each of
  the cables impedances.


Ignore the load and just think about the two cables joining at the "T" intersection. If both cables are 50 ohm then there is no problem - matching is perfect. However, when you add the load you are putting an extra 50 ohm in parallel with the previously joined and matched cables. This creates a reflection.

If you wished to join three cables of impedance/source 50 ohms together, the intersection would need three 16.67 ohm resistors to avoid reflections like this: -







simulate this circuit &ndash; Schematic created using CircuitLab

It's fairly easy to work out.