Quite a few of the decal setting solutions have vinegar in them. Some modelers use vinegar exclusively as a setting solution, but, have found out it is too diluted to do help decals snuggle down properly.
I found out by accident that the best setting solution is diluted alcohol, isopropyl or denatrued will do the job. Don't use it full strength, start with a 10% solution of alcohol and 90% water and go up from there.