I'm trying to use this command here, to simply get an item with a two word name, which works fine:

/give @p bow 1 0 {display:{Name:"my bow"}}

However, when trying to use another command block with /blockdata to insert that command into another block, I get an error.

/blockdata ~ ~2 ~ {Command:"/give @p bow 1 0 {display:{Name:"my bow"}}"}

This is the command I have, which will then give the following error:

[00:47:00] Data tag parsing failed: Expected '}' but got 'm' at: ..."/give @p bow 1 0 {display:{Name:"m<--[HERE]

Removing the quotations around the custom name will allow /blockdata to work, but the block to give you the bow will not.

Making the item's name only one word has been only solution thus far.

From the looks of it, 1.12's new error handling cannot handle double quotation marks anymore, because this command did work in 1.11.2