Struggling with multiline regex

We're collecting JBoss/Wildfly log output that seems pretty straightforward, but I'm having trouble getting the boundary regex to work such that I can capture exception stack traces as one logical message. Typical log lines are like this:

2015-05-22 20:57:44,471 INFO com.adaptive.adminservice.rest.AdminServiceRestImpl isAuthentic start

The regex I started with was pretty basic:

     \d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}.*\n+

This works for our Play logs which are very similar, and seems like it should match the above lines correctly. I've also tried variants without the \n, using groupings, using more restrictive rules for the message part of the regex, and pretty much everything else I can think of.

The result I get is either just no matching at all (one message per line even within stack traces), or one big message every time, where all the lines within a given time period show up in one message.

I'm quite confused. I actually though that sumo would be able to infer multi-lines based on this format, but that doesn't work either --- just drops every line into its own message.

I even hex-dumped the file to be sure the log had the line endings and stuff I expected, and it does.

Regex is always touchy, but it feels like I must be missing something --- any ideas? 

Thanks ...

---S