TDR unexpected results
When the far-end reflection returns, it causes a source reflection due to mismatch between source and cable impedance.
If you use thinner pulses, you can more easily see what happens: -

The simulation above uses a source impedance of 25 Ω and a line that is 50 Ω with an open far-end. The line is 10 metres long and is loss-less. If I make the pulse 200 ns you see this: -

Now, because you have reflections overlapping the original and reflections overlapping reflections, it becomes that much harder to analyse but, all the information is in there should you be prepared to work at it.
If I made the pulse 300 ns, the picture changes again but, the basic information is all in there: -


To change the cable parameters in microcap you need to access this by double clicking on the transmission line part and editing the line highlighted: -

This line has a length (LEN) of 5 metres with C/m and L/m also stated.