Data values/Block IDs – Official Minecraft Wiki

Lava replaces blocks generated in caves and ravines between level 1 and 10. Level 1 to 10 is considered "Lava Level" because this is where a player should be careful while mining. If the player creates a world without any caves or ravines, lava will not appear, and if lava lakes, strongholds and villages are disabled, the only source is the Nether. Lava will not replace air blocks inside , or between level 1 and 10.

Gears do not show up on non-solid blocks, but do on the Infinite Water Source and Infinite Lava Source, proving that they are solid blocks.

I don't have this problem, and my circuit is just the same as yours. Maybe you are still playing in a snapshot of 1.9 or something. If not you could try to go in another version like 1.8.9 and not 1.9. Otherwise your ID's of your lava are changing at the end of your second command block, I have tried this at my circuit, but it still works. I guess it will be your minecraft version, or some lagg by filling a large area.

Magma Block – Official Minecraft Wiki

Jul 6, 2017 - Obsidian is formed when flowing water hits a lava source block, and .. Lava above a nontransparent block (does include stairs, fences, and slabs) produces dripping particles on the underside of that block. These droplets are purely aesthetic, functioning identically to their water counterparts, except water particles are slightly faster.

Data values – Official Minecraft Wiki

Lava spends most of its time as stationary, rather than 'flowing' – regardless of its level, or whether it contains a current downwards or to the side. When specifically triggered by a block update, lava will change to 'flowing', update its level, then change back to stationary. Lava springs are generated as flowing, and lava lakes are generated as stationary.

Buckets can hold either Lava, Milk or Water

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Command : /give (username) (Item ID)
IDs : Water - 8
Still Water - 9
Lava - 10
Still Lava - 11
Monster Spawner - 52
Nether Portal Block - 90
Locked Chest (April Fool's) - 95
End Portal Block - 119
Ender Dragon Egg - 122
Original Tripwire - 132 (I figured out it is not string)
Written Book - 387
Half Of Wodden Door - 64
Blank sign - 63
Burning Furnace - 62
Floating Cocoa Plant - 127
Half Of Bed - 26
Farm Land (Soil) - 60
Fire Block - 51
Half Of Iron Door - 71
Piston Arm - 34

Items Non Mentioned
Unlit Redstone Torch - 75
Redstone Repeater On - 94
Redstone Lamp On - 124
Redstone Comparator On - 150

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Thank So Much For Watching.In , lava is extremely common, appearing more frequently than in . Seas of lava occur, with sea level at level 31, about a quarter of the total height of the Nether (as 63 is about a quarter the height of the Overworld). They extend down to about level 22 at the most. Lava also appears in single blocks inside the . In , lava is a renewable resource, due to the fact that the player can reset the nether in the world options.