dbmail/lmtpd Invalid utf8 character string

hello there,

recently upgraded dbmail to version 3.1.17 with opensuse 42.1 and 
mariadb 10.0.22

as far as i can tell all seems to be running fine.

but i discovered some lines in the error log:

2016-03-07T06:07:36.538895+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F8E'
2016-03-07T07:08:51.386313+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F8E'
2016-03-07T08:30:58.980281+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F8C'
2016-03-08T06:05:47.125641+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F95'
2016-03-08T07:08:54.918362+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F95'
2016-03-08T11:06:34.220121+01:00 cx20 dbmail/lmtpd[4034]: 
Error:[message] _header_value_get_id(+1540): SQLException: Invalid utf8 
character string: 'F09F91'

is this something i need to worry about?

thanks, greetings & all the best
becki