"Exceeded the size limit of 20000 characters." – but in fact, I didn't

Hi,
I'm creating a large MC question with 2000+ choices for the purposes of later randomization (I want to hide the question later on with JS and pipe in displayed choices). After attempting 'Edit Multiple' & pasting the choices, I'm confronted with the above error message – that I exceeded 20,000 characters. This is simply not true – not only b/c they are settlement names, and far too many settlements have a name with <10 characters in the country where the survey is fielded, but also b/c I checked: it's around 19,000 characters. Making the list smaller (i.e. cutting out some ~100 choices) gives me 18,000 characters, but I still get the error message.
What is going on? Why clearly <20K char long MC choice list gives me the above error message? Does this has anything to do with the original format of the answers list? (i.e. whether I copy-paste the choices from a csv, a tab separated document, etc.) As I want to use piped text later on, drill down is not an option for me (then I would be confronted with the warning/error "This Drill Down question has many answers. You will not be able to base any logic off this question.") Does anyone have an idea how to solve this?