Removing paste (I think!) off wallpaper

[bristol]

Hello

I purchased some rolls of Galerie Simply stripes and have hung it horizontally to create a wider impression in a room.
A couple of queries though which Galerie haven't answered on:
1- The paper I bought is brown and cream stripes but when it arrived I noticed a very thin cream stripe which must butt onto a thick cream stripe.
This means that for a moderate decorater like me, the join is much more visible than had it simply joined equal sized brown and cream stripes.
Any ideas why this additional stripe exists? - buggered if I can see any advantage at all.

2- Manin reason for this posting - the paper is pre pasted, but unfortunately didn't take in a few instances on the first drop, so I put on a thin spread of paste myself. This has made it adhere much better BUT - when I went over the paper with a clean sponge, a light film appeared which is highly visible on the brown stripes, and seems impossible to shift.
I was sure the sponge was clean - any thoughts on what this might be, and if so, how I get rid of it?

Cheers