Hi. I'm looking for help for recent issues I've had with my buttercream icing. I live in the south with high temps and high humidity. I use IndyDebi's recipe, which I love! I have used her recipe for probably 3 - 4 years with very good results. However, in the past 6-9 months I've had several issues. The icing is starting to separate (liquid pooling on the base of the tiers) after the cake is iced and crusted. I usually notice it the next morning if I've iced one overnight; happens on white or colored icing. (I've noticed this occur in the bowl after a couple of days, but never had any trouble on the cake unless it was 4-5 days old when only a few slices were left.). And, I notice the icing wants to slide from the cake much easier, even after crusted and dried. Other than using 1% milk sometimes, I've made no changes to the ingredients I use for the icing, or no changes to the types of cakes I'm putting the icing on. Most of my cakes are WASC style cakes, with only buttercream between the layers.  Below are the ingredients and brands I use for the icing.

Crisco, unflavored
Domino Powdered Sugar 10X
Dream Whip
Happy Home Flavoring (it's a locally available fundraising flavoring. I use 1 T clear butter and 2 T clear vanilla, which is imitation flavoring)
1% or 2% milk - generally a store brand from Wal-Mart or Winn-Dixie
I also add a pinch of salt, just to balance the sweetness a little.

Hope someone has a clue what may be the issue. I'm puzzled! Thanks for reading.