Dual extrusion - second extruder sometimes reversed

[TN Yankee]

I've been working with the SeeMeCNC dual extrusion Y, a Max V2 with accelerometer and running master 20170328. All my testing until tonight has been with extruder 0, which is an EZRStruder fed by a geared stepper. Using kraeger's steps elsewhere here, I got a pretty good set of extrudes & retracts figured out for the moment. I then switched (via Octoprint) to T1, which is an E3D Titan fed by my spare SeeMeCNC/Kysan motor.

T1 will *usually* run in reverse if an extrude command is proceeded by a G91 (relative mode). This is the case when being commanded via the Octoprint Control tab (for example a G91 \ G1 E-20 \ G90, will extrude 20mm). If I send just G1 E-20 via the terminal, it will *usually* retract. I say usually because there have been a few times when it will only retract, no matter if I send G90 or M82 beforehand.

There also have been a couple of times where my test gcode file commands T1 to extrude 20mm, and it instead retracts much more, possibly 200mm.

T0 does not exhibit this behavior.

What could be the cause? FWIW, I see in the latest master branch (which I'm not running), the CLONE setting has been removed. I have NUM_EXTRUDER set to 2, and CLONE set to 1 in my f/w.