Weird iRule issue with short hostname.

I have a use case where I needed to reject connections to port 990 on a VIP if the host comes in as a certain set of values. Since this is not http traffic, I am having to look at the TCP payload. The iRule works perfectly fine in all tested cases except one. If the host name is 2 letters or less, the connection just hangs up regardless of if it is the datagroup to be rejected or not. Hostnames of 3 letters are longer work fine and are allowed or rejected based off of if they are in the DG or not. I added some logging and the 2 letter host name is included in the TCP payload and it looks correct so i am not sure what the issue is

For example:

ab.domain.com does not work if the iRule is applied to the VIP even if it is in not in the DG

abc.domain.com works or is rejected as expected depending on if it is in the DG or not

abcd.domain.com works or is rejected as expected depending on if it is in the DG or not

when CLIENT_ACCEPTED {
  TCP::collect 250
}
when CLIENT_DATA {
log local0. "TCP payload contains [TCP::payload 250]"
if {[matchclass [TCP::payload 250] contains FTPSReject] } {

reject
  log local0. "TCP payload rejected"

}
TCP::release
}