My original post: Exposed filters group: increase weight sort count (#delta)
This still hasn't been fixed at the time of this writing. So here we go...
Sort breaks, and does unpredictable sorting, if you use more than 20 options. E.g. say you have have an exposed grouped filter with a price drop down of more than 20 options, sorting will not work after 20 items, it will always spit out a different order than what you specify.
Edit the following Views module file:
Look for this:
'#delta' => 10
Replace with this:
'#delta' => 60