Are lower case sub-headings a common formatting convention? I recently presented a poster at an undergraduate research conference, and they are now soliciting write-ups for the conference proceedings. I was surprised at their formatting guidelines, specifically the requirement that all sub-headings be lower case. Ex.:

1. Main Heading
  1.1 this is a secondary heading
    1.1.2 this is a tertiary heading 


I have never seen this convention. I've always thought the preferred style for sub-headings is to either use the same capitalization format as for main headings, or capitalize the first letter of the first word.

I find this all-lower case format to be unprofessional-looking, and was wondering: is this a common convention, and if so, what is the underlying rationale?
I have never in my academic life seen this convention: I have always seen lower-level sub-headings follow exactly the same convention as higher-level headings.

Do what they tell you to do (the world has lots of strange Official Requirements for Our Unique And Special Snowflake Publication Venue), but I wouldn't worry about it for anywhere else in life.