I tested a stereo connection (two cable inserted) on Space input but with right channel muted. On stereo output (fully wet no dry signal) I had the audio of the left channel input on both outputs. (I assume Space treats the signal as a mono source, even with two cables on input). Then I unmuted the right channel and still had the left input on the right output channel. I was expecting to hear the left input only on the left output and the same with the right channel. Is this the normal behaviour for wet signal or am I missing something?
It is normal. You said you turned the MIX to 100 so there is no dry signal. The wet processed signal of input 1 will appear in both outputs depending on the current algorithm and your parameter settings.
Manual states this regarding dry signal: SPACE detects which input and output jacks have cables plugged in and routes audio I/O accordingly. With a Mono Input (Input 1) and Stereo Outputs, the dry contribution for both outputs comes from the Mono Input (Input 1). With Stereo Inputs, the dry contribution at Output 1 is from Input 1 and the dry contribution at Output 2 is from Input 2, thereby maintaining the original signal stereo image.
Again, it describes that the pedal detects if the inputs are plugged, not if muted or not. It tells how dry signal is processed. But in your case you said you set your pedal fully wet not dry signal.