From pcre changelog, version 7.0:

4. Fixed a major bug that caused incorrect computation of the amount of memory
    required for a compiled pattern when options that changed within the
    pattern affected the logic of the preliminary scan that determines the
    length. The relevant options are -x, and -i in UTF-8 mode. The result was
    that the computed length was too small. The symptoms of this bug were
    either the PCRE error "internal error: code overflow" from pcre_compile(),
    or a glibc crash with a message such as "pcretest: free(): invalid next
    size (fast)". Examples of patterns that provoked this bug (shown in
    pcretest format) are:

      /(?-x: )/x
      /(?x)(?-x: \s*#\s*)/
      /((?i)[\x{c0}])/8
      /(?i:[\x{c0}])/8

    HOWEVER: Change 17 below makes this fix obsolete as the memory computation
    is now done differently.

Acknowledgements:

Red Hat would like to thank Ludwig Nussel for reporting this issue.