Sorry I didn't explain myself better; I thought that someone else might have noticed this and have a solution. I'll grab some pictures of Moo's Mews in base-game and M&G to show you... give me a minute.
This problem occurs for any CFE'd wall with a non-uniform wall covering, but Moo's Mews Pool really shows the difference. Here's the pool as I designed it:
Notice how I designed the pool to have a white border at the bottom of the roof, to help define the roof from the rest of the building? Now, look at the same roof in M&G:
I've left the wall covering designer up so that you can see how I am now getting the multi-colored stripe at the top of the wall covering, rather than the white stripe at the bottom.
One obvious solution for this roof is to separate it into two sections: one for the white stripe and one for the plain blue wall. However, that won't work for lots where I want to use the pattern on the bottom of a wall.
I'm just disappointed that EA is so inconsistent between EPs. Each EP seems to break things that used to work in previous EPs.