As I mentioned, this is not a scientific test but rather just something that I have tried from time to time and has always (shockingly in my opinion) failed but today worked. It takes a minute of two of prompting, is boring to verify and I don't remember exactly which models I have used. It is purely a personal anecdote, nothing more.
However, looking at the code that Gemini wrote in the link, it does the same thing that other LLMs often do, which is to assume that we are encoding individual long values. I assume there must be a github repo or stackoverflow question in the weights somewhere that is pushing it in this direction but it is a little odd. Naturally, this isn't the kind encoder that someone would normally want. Typically it should encode a byte array and return a string (or maybe encode / decode UTF8 strings directly). Having the interface use a long is very weird and not very useful.
In any case, I suspect with a bit more prompting you might be able to get gemini to do the right thing.