&dateFormat=`%b <br /> %e`
&dateFormat=`%b <br /> %d`
What locale is your PHP install set to?
Not all conversion specifiers may be supported by your C library, in which case they will not be supported by PHP’s strftime(). Additionally, not all platforms support negative timestamps, therefore your date range may be limited to no earlier than the Unix epoch. This means that e.g. %e, %T, %R and %D (there might be more) and dates prior to Jan 1, 1970 will not work on Windows, some Linux distributions, and a few other operating systems.
Try it in a straight php file outside of modx and ditto. This may be related to your OS.you are right...