In a Mixpanel funnel report with a breakdown, a user will be counted in each breakdown segment in which they qualify. This means that if a user loads a page from more than one category (breakdown value) within the funnel's timeframe, they can be counted in multiple segments. However, they are not double-counted within a single segment; rather, they are counted once per qualifying segment.
For example, if your funnel is broken down by "category" and a user loads pages from both "Electronics" and "Clothing" before making a purchase, that user will appear in both the "Electronics" and "Clothing" segments of the breakdown. This is by design: "Users will count in each breakdown segment in which they qualify" Funnels Advanced Concepts: Breakdowns.
This can result in the sum of users across all segments being greater than the total number of unique users in the funnel, because a single user can contribute to multiple segments if they meet the criteria for each.
So, to directly answer your question: the funnel report does not "double count" an order within a single segment, but a user (and their conversion) can appear in multiple segments if they qualify for more than one breakdown value during the funnel timeframe. This is expected behavior in Mixpanel's funnel breakdowns.
