It appears that with the majority of the available stencils in the Drawing Table, many of the selections' images are scaled incorrectly. A few of them are fine.

Minecraft version: 1.7.10
Forge version: 10.13.3.1407-1.7.10
Mods being used:

No extra information, no reproducible. Closing.

They are all oversized. Some of them look correct even when doubled, but they still have wrong size. Here how first one should look like:

I can't reproduce that one, so I guess it's interaction with one of items in inventory or other mods. Try with empty inventory and then with disabled NEI.

I have removed all of the mods except for OpenModsLib and OpenBlocks itself. I'm still getting the same issue:

Sorry, I still can't reproduce (even after adding NEI). Though I haven't tried optifine, but that's generally unsupported. Please make sure you have most recent version of all mods, directly from openmods.info (OB is at 1.4.3, OM 0.7.3)