Homing problem

I found the following two issues when I repeated doing homing operation:

1. The homing operation could sometimes fail to complete correctly. A typical outcome when that happens is that, the motor would not reach the specified Zero Back-off position. For example, instead of drive a further Zero Back-off of 14 mm after the switch was released at the coordinate about -4mm, it only moved about 4 mm when the coordinate went to 0. In this situation, the TinyG seems to know the table coordinates correctly but for some reason it stops early before the specified Zero Back-off was reached. For a reason unknown to me, if I reduce the current limit to that axis to a lower value, the homing operation can then be completed correctly. I don’t understand that why the higher current would make it incorrect, but the lower current could make it work? Also, the current limit that made the homing work last time may fail to work in a few days like what happend to me today, and I needed to lower the limit again to make it to work. Would you be able to advise why the homing operation would perform like this, and what should I do to ensure a reliable homing operation?

2. The current limit for each axis seems not independent to each other. When I adjusted the current limit of axis X via its potentiometer, it also affected the actual current in axis Y, is it what you would expect? Or how to ensure an independent adjustment of current limit for each axis?