Summary:
Quark's 'merge nearby' feature works as expected with ImmersiveCraft chests, but not ImmersiveCraft shelves.

The author of the original issue believed this behavior may be due to Quark looking for IInventory and behaving in a hardcoded manner for 'Chest'-named blocks. He also noted that ImmersiveCraft implements ISidedInventory.

It's unclear to me what is causing the incompatibility. McJty, following the original author's analysis (if not his own?) has, for now, suggested Quark's behavior may be responsible.

I have quite a bit of respect for both Vazkii and McJty and am confident a solution can be found.

Versions:
Minecraft 12.2
forge-1.12.2-14.23.2.2635
Quark-r1.4-122
immcraft-1.12-1.4.1
Behavior experienced in the SevTech Ages modpack version 3.0.0-3.0.4.