$ pcretest 
PCRE version 8.13 2011-08-16

  re> /(?>(?&t)c|(?&t))(?(DEFINE)(?<t>a|b(*PRUNE)c))/s
data> ba
Error -26 (nested recursion at the same subject position)
data> bba
^C
[loop]

While pcre-8.12 gives:

$ pcretest 
PCRE version 8.12 2011-01-15

  re> /(?>(?&t)c|(?&t))(?(DEFINE)(?<t>a|b(*PRUNE)c))/s
data> ba
 0: a
data> bba
 0: a
data> 


This is regression reported to upstream.