I set-up a level 10 gym today. After hitting 50,000, I wanted to bump prestige up a little more but could not. A few hours later the gym was briefly attacked and prestige fell to 47,000. I fought back and raised prestige to 49,000, then left for a few hours.
Someone chipped-in with gym defense and currently, the prestige level is exactly (52,000 / 50,000). How is this possible when I couldn't go above 50,000?