How can I get the fields in the lead to opportunity sales process to appear as checkboxes and not dropdown list?

Hi, 

In my lead to opportunity sales process flow I have made several custom fields with datatype choice yes/no. I want them all to appear as checkboxes, but for some reason the fields randomly get either checkbox or dropdown list. 



Does anyone know why this happens and how I can change the formatting? 

I have tried to add them to the form and changed controls and checked the xml in solution to check if there was a difference in the fields there, but no luck.