Sometimes there are bugs in interpreters that make them unable to run programs that are valid by the specification of the language, or make them work incorrectly.
This will break programs using those features, which can be frustrating especially in code golf.
For example, let's assume that in the docs for the language Lang it says:
Return a copy of the string with all the cased characters converted to uppercase.
But then, when you try it:
>>> 'test'.upper() 'Test'
Assuming that all available interpreters have some bug that prevent the program from working, but the specification still defines how that program should work, will such bugs make such a program invalid if
- the interpreter is never fixed?
- the interpreter is fixed after the challenge is posted?
- the interpreter is intended to be fixed at some point after the challenge is posted?
In none of the cases could the program be run in an interpreter released before the challenge is posted, which is generally thought to be a requirement.