AudioMatt

active 

0/1 [int] If the target_seq attribute is set to zero, the message active 0 deactivates all sequences. The word active, followed by any non-zero value, will activate all sequences. If the target_seq attribute is set to a value greater than zero, the message active 0 deactivates the specified sequence. The word active, followed by any non-zero value, will activate the specified sequence.

If you try this in the live.step help file it doesn't work.

[target_seq 1, active 1, target_seq 2, active 1] 

activates sequence 2 and deactivates sequence 1

seems like you're losing an arbitrary amount of flexibility here, why only have the option of activating all or one sequence?

Note: Checked the 8.1.6 bug fixes , it's not mentioned there.

    "version" : "Version 8.1.5 (9359645) (64-bit mac)",

    "osversion" : "Mac OS X Version 10.14.5 (Build 18F132) x86_64",

    "scheduler_in_audio_interrupt" : "on",

    "audio_drivername" : "Core Audio",

    "machine_id" : "66d5ed6deae16e8412e19294b0118550",

    "refreshrate" : 33.333332061767578,

        "CNMAT Externals" : "1.0.4",

        "Node For Max" : "1.3.2",

        "Video & Graphics" : "7.2.0",

        "zsa.descriptors" : "1.2.0"

[target_seq 0, active 1] WORKS
[target_seq 0, active 0] WORKS
[target_seq 1, active 1, target_seq 2, active 1]  activates sequence 2 and deactivates sequence 1


{
	"version" : "Version 8.1.5 (9359645) (64-bit mac)",
	"platform" : "mac",
	"arch" : "x64",
	"osversion" : "Mac OS X Version 10.14.5 (Build 18F132) x86_64",
	"samplerate" : 48000,
	"iovs" : 128,
	"sigvs" : 128,
	"scheduler_in_audio_interrupt" : "on",
	"audio_drivername" : "Core Audio",
	"audio_driver_subname" : "",
	"license" : "permanent full",
	"machine_id" : "66d5ed6deae16e8412e19294b0118550",
	"eventinterval" : 2,
	"schedinterval" : 1.0,
	"overdrive" : "on",
	"pollthrottle" : 40,
	"queuethrottle" : 100,
	"sysqelemthrottle" : 1000,
	"refreshrate" : 33.333332061767578,
	"schedslop" : 25.0,
	"eventprobing" : 0,
	"mixerparallel" : "off",
	"mixercrossfade" : 0,
	"mixerlatency" : 30.0,
	"mixerramptime" : 10.0,
	"videoengine" : "avf",
	"glengine" : "gl2",
	"packages" : 	{
		"BEAP" : "1.0.3",
		"BLOCKS" : "1.2.7",
		"CNMAT Externals" : "1.0.4",
		"cv.jit" : "1.8.0",
		"ease" : "1.1.1",
		"ejies" : "3.2.4",
		"hap" : "1.0.6",
		"jit.mo" : "1.1.2",
		"mat.oo" : "1.0.0",
		"max-mxj" : "7.2.5",
		"mi-gen" : "1.1.0",
		"Mira" : "1.2.1",
		"ml.lib" : "1.1.1",
		"Node For Max" : "1.3.2",
		"sensel" : "0.4.1",
		"VIDDLL" : "1.2.3",
		"Video & Graphics" : "7.2.0",
		"Vizzie" : "2.0.3",
		"zero" : "1.0.3",
		"zsa.descriptors" : "1.2.0"
	}

According to the Live.step reference,
active 

0/1 [int] If the target_seq attribute is set to zero, the message active 0 deactivates all se

[BUG] [live.step] activating multiple specific sequences impossible