Apparent ambiguous interpretation of parser rule names

[The-Futurist]

I have two parser rules, if and iF but use of the latter seems to lead to an exception when the generated Java is compiled. If I rename rule iF to say iX the problem goes away. This suggest that despite if and iF being legal distinct names, something in the generated Java is making some assumptions.

Exception in thread "main" java.lang.NoClassDefFoundError: SyscodeParser$IfContext (wrong name: SyscodeParser$IFContext)
at java.base/java.lang.ClassLoader.defineClass1(Native Method)
at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1013)
at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)
at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
at java.base/java.lang.Class.getDeclaredConstructors0(Native Method)
at java.base/java.lang.Class.privateGetDeclaredConstructors(Class.java:3429)
at java.base/java.lang.Class.getConstructor0(Class.java:3634)
at java.base/java.lang.Class.getConstructor(Class.java:2324)
at org.antlr.v4.gui.TestRig.process(TestRig.java:151)
at org.antlr.v4.gui.TestRig.main(TestRig.java:119)