I'm having problems with classes not syncing when a variable is attached to the class.

1. I have class sync turned on in the plugin
2. I have checked to ensure no existing duplicates of any classes
3. All classes sync fine when no variables are attached to any class
4. When I attach a simple font family variable to a heading/text class, duplicate classes are created (eg. Setting a font-family variable on heading-style-h1)
5. Strangely, some other classes are synced just fine when variable is attached (eg. If I attach a size variable to the max-width property of container-large)

Am I doing something wrong here or is this a known issue?
Thanks!