In the past when I started making cakes (with simple syrup) and I never refrigerate my cakes and my cakes never bulge, but ever since I started to refrigerate them 75% of the time they do bulge. So I have a cake I’m working on for Saturday and I’m putting myself to the test and not refrigerate and see and see what happens. Then I saw a video on YouTube saying if you do refrigerate stick a small skinny down the middle of the cake before fondant so the moisture can escape that way, so next order I’ll do the whole trick. (shrugs)

 in my experience both ways, cold and never cold produce the air bubbles so when i remember i put a small poke hole in as hidden a spot as possible all the way through the icing into the cake in every layer and leave the holes open so the air can escape -- 

It also depends how long you refrigerate your cakes. I don't put fondant on a cake unless it's been in th fridge for at least 12 hours. I've tried after 4 to 8 hours and it doesn't work for me.