Get MMF smooth.
What does your cake look like immediately before covering with fondant?
Ok, based on this picture: http://cakecentral.com/gallery/1988032 your buttercream smoothing skills seem to be ok. Are you making sure that the cake you are going to cover in fondant is this sharply finished? Because according to this picture: http://cakecentral.com/gallery/1692374 I'm guessing not. I will assume you are using a crusting buttercream? I use a meringue buttercream, and I chill my tiers rock hard solid before putting very thin fondant on. The buttercream doesn't squish around, and the edges stay sharp and neat, and the sides remain smooth, and I get aflawless finish.
But the most important thing of all, I make sure the cake is perfectly smooth, level, and sharp before putting fondant on. This means, they are as good as they would look if they were not going to be covered. A bumpy lumpy uneven cake will show thru fondant.
And I use MFF, not MMF, but that matters not.
After I have rolled out the MMF I take a fondant smoother and run over the fondant before I put it on the cake, kinda like ironing the fondant.
Another option you could try is chocolate ganache under your fondant. It forms a nice hard shell around your cake so you always have a smooth surface for your fondant. Or could it be your fondant? Is it smooth when you roll it out? MMF is super finickity especially in humid climates. When I first started with MMF I would always have trouble rolling it out.
I see you are in sunny humid Florida. I can relate. Yesterday the humidity here was 72%. I have purchased Satin Ice. I found that when it is on sale, the cost is almost the same is if I make home made MMF.
Prior to purchasing the Satin Ice, I actually had to add a tiny bit of corn starch to dry up the home made mmf a bit. I realize many would say this is a MMF taboo, but I had to do what I had to do to get something workable.
I make my mmf a bit stiffer than most. 6lbs of ps to 2lbs and knead in every bit of it too. No more than a total of 8 tblsp of liquid (water and flavoring). It takes a bit more kneading to get it soft the next day but its' workability is worth it to me.
Its not a cake icing issue - it's the fondant itself. It's got bubbles in it. Tiny little bubbles and some on the surface, as if it 'popped' there. In other words, theres a small divot on the fondant where a bubble use to be. I tried everything! Changing brands of marshmallows, different brands of powdered sugar, stirring the marshmallows enough before adding the powdered sugar to ensure that I got rid of the air that the marshmallows hold, even being careful not to knead excessively in case that was trapping air. And it IS worse with the humidity! Love the taste of MMF (I always flavor it according to the cake's flavor) but can't seem to get it smooooth. Sometimes it's smoother than others but never SMOOTH. Like SatinIce or Wilton smooth.
What could it be??
Does the humidity really make that much of a difference? I live in South Louisiana and I have never had a problem with my MMF? I use domino powered sugar and kraft marshmallows and it has come out fine every time, guess I'm lucky so far.
It doesn't make a difference for me when I have the a/c running. It doesn't always get turned on though...even in the hottest part of the summer (spent a long time in Hell...I mean Texas...and even at its' hottest here, doesn't come close in comparison...therefore, I don't always run the a/c)
I had this problem this past week and it was the first time my fondant was "bubbly" like that. I kneaded it a LOT, then let it set overnight. The next day it was better, but I had to knead it again first. Still not sure exactly why it happened, though!
I tend to get air traped in mine, especialy if I have started to roll it and for some reason have to start over and fold it back up.
Could it be that the crisco is somehow making this happen? If you crisco/grease your MMF before rolling, it essentially hydroplanes across the surface and can't get smooth enough.. sometimes that happens with me.
Instead, I take the crisco and put a thin layer on my countertop... but then I dust it (almost like cake release for baking) with confectioners' sugar/cornstarch and it makes it smooth every time.