"runtest.php" API is appending characters to Test ID

[performanceed]

Hello WPTers,

I am pretty familiar with WPT's RESTful API's but today I encountered something I've never seen before. I am hitting <wptserver>.com/runtest.php?<my query params> and it is returning a test ID with characters appended to it.

Example:
Normal ID: 180928_DEVi9E_6
Weird ID: 180928_DEViVV_b68aa21b460fbe7675a81002d5

Does anybody know why this is happening? It's breaking my integration.

Thanks!
-e