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diff --git a/tests/custom/99_bugs/12_altblock_stack_mismatch b/tests/custom/99_bugs/12_altblock_stack_mismatch
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+When compiling alternative syntax blocks, such as `for ...: endfor`,
+`if ...: endif` etc., the compiler didn't assign the contained statements
+to a dedicated lexical scope, which caused a stack mismatch between
+compiler and vm when such blocks declaring local variables weren't
+actually executed.
+
+-- Expect stdout --
+2
+-- End --
+
+-- Testcase --
+{%
+	if (false):
+		let a = 1;
+	endif;
+
+	/* Due to lack of own lexical scope above, the compiler assumed
+	 * that `a` is still on stack but the code to initialize it was
+	 * never executed, so stack offsets were shifted by one from here
+	 * on throughout the rest of the program. */
+
+	let b = 2;
+
+	print(b, "\n");
+%}
+-- End --
+
+
+Test a variation of the bug using `for in..endfor` loop syntax.
+
+-- Expect stdout --
+2
+-- End --
+
+-- Testcase --
+{%
+	for (let x in []):
+		let a = 1;
+	endfor;
+
+	let b = 2;
+
+	print(b, "\n");
+%}
+-- End --
+
+
+Test a variation of the bug using `for..endfor` count loop syntax.
+
+-- Expect stdout --
+2
+-- End --
+
+-- Testcase --
+{%
+	for (let i = 0; i < 0; i++):
+		let a = 1;
+	endfor;
+
+	let b = 2;
+
+	print(b, "\n");
+%}
+-- End --
+
+
+Test a variation of the bug using `while..endwhile` loop syntax.
+
+-- Expect stdout --
+2
+-- End --
+
+-- Testcase --
+{%
+	while (false):
+		let a = 1;
+	endwhile;
+
+	let b = 2;
+
+	print(b, "\n");
+%}
+-- End --