On pressing Xfer for any material, (I have seen it on water or monopropellant), from a full tank to a not full tank, it happens that full tank is overfull (for example, 1501/1500) .Then, you cannot perform any transfer of this material in the station. Transfer amount cannot be edited, and setting bar cannot be moved.

Does this mean that the tank you are filling ends up overfull?

On the contrary, the tank I am emptying became overfull. I guess for any reason, a function is returning -1, and it is removed for tank volume.

Thanks for the feedback. I'll investigate :) I thought I had squashed that bug ages ago...

This has been corrected with release 0.90.0_4.0.2