boost::asio::async_read_until with regex and timeout - strange behaviour - c++

Question

Based on code from a Boost example (http://www.boost.org/doc/libs/1_46_1/doc/html/boost_asio/example/timeouts/blocking_tcp_client.cpp)
I made a function read_expect() as follows:
std::string TcpClient::read_expect(const boost::regex & expected,
boost::posix_time::time_duration timeout)
{
// Set a deadline for the asynchronous operation. Since this function uses
// a composed operation (async_read_until), the deadline applies to the
// entire operation, rather than individual reads from the socket.
deadline_.expires_from_now(timeout);
// Set up the variable that receives the result of the asynchronous
// operation. The error code is set to would_block to signal that the
// operation is incomplete. Asio guarantees that its asynchronous
// operations will never fail with would_block, so any other value in
// ec indicates completion.
boost::system::error_code ec = boost::asio::error::would_block;
// Start the asynchronous operation itself. The boost::lambda function
// object is used as a callback and will update the ec variable when the
// operation completes. The blocking_udp_client.cpp example shows how you
// can use boost::bind rather than boost::lambda.
boost::asio::async_read_until(socket_, input_buffer_, expected, var(ec) = _1);
// Block until the asynchronous operation has completed.
do
{
io_service_.run_one();
}
while (ec == boost::asio::error::would_block);
if (ec)
{
throw boost::system::system_error(ec);
}
// take the whole response
std::string result;
std::string line;
std::istream is(&input_buffer_);
while (is)
{
std::getline(is, line);
result += line;
}
return result;
}
This works fine when I use it with a regular expression
boost::regex(".*#ss#([^#]+)#.*")
, but I get strange behaviour when I change the regex to
boost::regex(".*#ss#(<Stats>[^#]+</Stats>)#.*")
, resulting in no timeout, causing the thread to hang on the async_read_until() call.
Maybe this is some silly error I cannot see in the regex, and I could use the first version, but I would really like to know why this is happening.
Thanks for any insight,
Marleen