The hob script will not use the results of a full parse in order to get itself boot strapped. 

The hob script appears to change only two variables:
   BB_ENV_EXTRAWHITE
   DISABLE_SANITY_CHECKS

You can duplicate the problem by doing the following:

mkdir proj
cd proj
. ../oe-init-build-env
bitbake -p
# Notice the parse is complete
# Now start "hob" with the "hob" command
hob

# Notice that it will immediately go to work with a full new parse

EXTRA INFORMATION:
I found that if I added "DISABLE_SANITY_CHECKS BB_ENV_EXTRAWHITE" to BB_HASHCONFIG_WHITELIST in the meta/conf/bitbake.conf that the parse data would get reused, but this is probably is not really the way to to fix this problem.  It seems that perhaps the DISABLE_SANITY_CHECKS should be in the default white list and that the hob script should be modified so as not to change the BB_ENV_EXTRAWHITE.