You're right, it has something to do with clock command:
Here is an outline of my trial
tclsh
% set ugly_date "2002-06-05 15:36:36+08"
2002-06-05 15:36:36+08
% clock format [clock scan $ugly_date] -format "%B %d, %Y %r" -gmt true
unable to convert date-time string "2002-06-05 15:36:36+08"
I tried a little experiment
% set ugly_date "2002-06-05 15:36:36"
2002-06-05 15:36:36
% clock format [clock scan $ugly_date] -format "%B %d, %Y %r" -gmt true
June 05, 2002 03:44:36 PM
It seems removing the +08 fixes the problem.
