The problem is that the author used the wrong function to send a warning to the 
user about truncation of data.  push_warning() takes a constant string and 
push_warning_printf() takes a format and variable arguments to fill it.

Since the string we were complaining about contains percent characters, the 
printf() code interprets the "%Y" et c. that the user sends.  That's wrong, and
often causes a crash, especially if the date mentions seconds, "%s".

A alternate fix would be to use  push_warning_printf(..., "%s", warn_buff) .