Currently, to interact with the issue tracker, you need to be invited to the repository, thus counting against the available max-users limit of whatever plan you have. Assuming the intent is for the price plans to reflect the number of developers on the project, this does seem counterproductive, as a closed project either needs to pay for a priceplan counting every user and not just developer. Or, alternatively, find someplace else to communicate with users.
If it really is the intent to count users only participating issue tracking, the priceplans suddenly comes off as rather expensive.
My suggestion is to implement separate access rights for the repository itself and for the issue tracker, and only count users that are given any access to source (or more leniently are given write access to source).