Self interpreters don't work, whose bug is it?

[pimlu]

Problem

Running all the self-interpeters I've tried have failed to work in practice. Obviously there's two scenarios: my interpreter is broken, or their self-interpreter is broken. (or both...)

I've exhaustively tried all of them without success. Here is the status of each: (list comes from this SO question)

• 48-Lomont - interpreter encounters an infinite loop at the state 7³23^2586672442941¹43^5173344889847²⁷61^25866724441171¹
• 84-Amadeus - works for a single fraction, 2 fractions hits an infinite loop (this is demo2 in the Haskell code)
• 1779-Beder - assumed working, my program isn't smart enough to run this beast (never terminates, even on the smallest input I could construct)

Solution ideas

My problem is, my interpreter works on every program I can construct or run normally, but fails on a couple programs too large to run anywhere else. I want to prove or exclude my own interpreter as the root cause, but I'm not sure how yet.

The next thing I was thinking of was a fuzzer, but it seems unlikely to randomly generate useful control structures representative of a 50-fraction program, at least with a naive fuzzer.