When testing ABL on my Prusa 10" i3v with Ramps 1.4, I encountered a problem. I was using Proterface to manually send G28 and G29 commands to my printer and found if I delayed sending a G29 command following the sending of a G28 command I would get an error message "echo: Home X/Y before Z" and the ABL would run. The minimum interval that I measured that would produce this failure was exactly 60 seconds from the time the Z sensor retracts upon finishing the G28 command and the instant G29 is submitted. A minute is an abnormal amount of time between these two commands but it made me wonder if others had gotten caught by this issue while testing, and for my own curiosity what causes it?