Including an embedded text expression "[somevar]" in a text("[][]", arg1, arg2) call causes a compiler crash. ie:
return text("[src]'s foobar: [][]", foo, bar)
This is a very odd way to use a text proc, which itself is odd to use directly since embedded expressions compile down to text() procs, but it 'technically' complies with the spec, in that nothing suggests text() is anything more than a regular proc you can pass embedded strings too.
from byond convos this is likely related to the #undef fix.
work around would be to move the embedded expression ("[src]" in this case) over to the text argument lists