Arrow in failure messages does not point to the correct location in case of groups (aou,a)

[basbossink]

example:

"     c--a--b----"
"     ---(s,s)-(s,s)--(s,s)--"

leads to message:

System.Exception
Unexpected event received at time 6 on sequence 
   ---(s,s)-(s,s)--(s,s)--
         ↑

Expected output is:

System.Exception
Unexpected event received at time 6 on sequence 
   ---(s,s)-(s,s)--(s,s)--
                 ↑