async exceptions versus return in try in synchronized

The following is narrowed down from com.sun.naming.internal.FactoryEnumeration,
method next()

In the following code, a RuntimeEcception occurring at
instruction 8 or 9 will cause a redundant monitorexit.
The join point with mismatching monitors causes a C1 assertion failure.

frog:~/gjc-work/j2se-tl $ cat -n T.java
     1 class T {
     2 static int f(Object o, int x) {
     3 synchronized (o) {
     4 try {
     5 return x;
     6 } catch (RuntimeException e) {
     7 throw e;
     8 }
     9 }
    10 }
    11 }
frog:~/gjc-work/j2se-tl $ newjavac T.java
frog:~/gjc-work/j2se-tl $ javap -c -l T
Compiled from T.java
class T extends java.lang.Object {
    T();
    static int f(java.lang.Object, int);
}

Method T()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 return

Line numbers for method T()
   line 1: 0

Method int f(java.lang.Object, int)
   0 aload_0
   1 astore_2
   2 aload_2
   3 monitorenter
   4 iload_1
   5 istore_3
   6 aload_2
   7 monitorexit
   8 iload_3
   9 ireturn
  10 astore_3
  11 aload_3
  12 athrow
  13 astore 4
  15 aload_2
  16 monitorexit
  17 aload 4
  19 athrow
Exception table:
   from to target type
     4 10 10 <Class java.lang.RuntimeException>
     4 8 13 any
    10 17 13 any

Line numbers for method int f(java.lang.Object, int)
   line 3: 0
   line 5: 4
   line 7: 10
   line 9: 13
frog:~/gjc-work/j2se-tl $