I'll report this to the devs for them to take a look at... maybe user inputted data is not properly being trimmed like it should be.
update:
This has been fixed in the DEV branch and next release will fix the problem. In the mean time: User jpowers40828 PMed me and asked me to add this to the thread.
I was getting the same error and added a line to open.php to fix the problem. If you find the code below, it starts at line 20. Add the $vars = trim($vars); line in and you should be good.
if($_POST):
$vars = $_POST;
$vars=$vars=0; //Just Making sure we don't accept crap...only topicId is expected.
$vars = trim($vars); //clean email address