I don't know if this is still going on, I don't wanna revive old threads, but I've found a fix for this issue.
First off you need to make sure your google calendar or fbcal.com is unchecked :
-go to phone's menu, select calendar, hit 'menu' button, select 'more', go to 'calendars', uncheck google calendar (it may be displayed as gmail calendar)
After you have done that, uninstall your facebook for Android (you can install it later) is order to unsync your contacts so there will be no pics assigned.
Now comes the important part :
-go to phone's menu, select 'people', slide the screen selector over to 'online directories', select 'facebook', sign in........and you're done. Now you've activated "Facebook for HTC Sense", it's gonna sync by itself, the pictures will be crystal clear (will have the small blue facebook 'f' in the bottom left corner)
You can now install facebook for android back on your phone, but make sure you don't sync your contacts, or else you'll be back where you started !
Hope it helps !