Undocumented cleanroom requirement - only plascrete blocks in southeast corner

[MauveCloud]

I was having trouble figuring out why I was stuck on "incomplete structure" with a simple minimum-size cleanroom, until I looked closer at this loop:

GT5-Unofficial/src/main/java/gregtech/common/tileentities/machines/multi/GT_MetaTileEntity_Cleanroom.java

Lines 74 to 81 in 77a3c95

	for (int i = -1; i > -16; i--) {
	Block tBlock = aBaseMetaTileEntity.getBlockOffset(x, i, z);
	int tMeta = aBaseMetaTileEntity.getMetaIDOffset(x, i, z);
	if (tBlock != GregTech_API.sBlockReinforced || tMeta != 2) {
	y = i + 1;
	break;
	}
	}

That checks the southeast corner specifically for plascrete blocks to determine the height, so if I put an energy or maintenance hatch there (or less likely a machine hull, since there would be no directly adjacent basic machine for it to transfer energy/items to/from), it messes up the height calculation, and produces "incomplete structure".
Once I moved my energy hatch from the southeast to the northeast corner (and put a plascrete block where it had been), the "incomplete structure" message went away. However, I don't understand why that should have been necessary.

BTW, before anyone suggests copying code from GTNH to fix this, I've looked, and that particular loop is the same there.