AMPscript in Subject Line breaks in A/B Test email

Question

We sent out an A/B test email with the following subject line:

%%[IF NOT EMPTY(NM_FIRSTNAME) AND LENGTH(NM_FIRSTNAME) > 1 THEN ]%%
%%NM_FIRSTNAME%%, s
%%[ ELSE ]%%S
%%[ ENDIF ]%%ee your super in Product Name

The email sent without issue, however when the 'winning' email was sent, then the email failed to send.

After investigation it appears to be an AMPscript related issue, as we can see that the subject line changed to:

%%[IF NOT EMPTY(NM_FIRSTNAME) AND LENGTH(NM_FIRSTNAME) > 1 THEN ]%%
%%NM_FIRSTNAME%%, s
%%[ ELSE ]%%S
%%[ ENDIF ]%%ee your super in Product Name

Note the > character replacement. Has anyone seen this before and if so, do you know of a workaround?

Refer to screenshots below from Send Tracking pages.

A/B Test Send

Winning Email

Note no emails were sent.

Answer 1

Not sure why that happened in the winning email. Looks like a bug.

I suppose you could try moving the subject line conditional to a script block in the email.

Something like this:

Init block in the email

%%[ /* Modify to view AMPScript <div style="display:none;"> */

var @fn, @subject
set @fn = AttributeValue("NM_FIRSTNAME")

IF NOT EMPTY(@fn) and LENGTH(@fn) > 1 THEN
 set @subject = concat(@fn,", s")
ELSE 
  set @subject = "S"
ENDIF

set @subject = concat(@subject, "ee your super in Product Name")

/* </div> */
]%%

Subject

%%=v(@subject)=%%