You have to remember that the 100 limit does also count milbucks from replies to topics you have started.
So if you have started several popular topics, you can get a lot of milbucks from them each day, and your 100 limit can be reached quite fast.
If you want to check this you have to write down the amount of MilBucks you have when you log off each day, and compare it to the amount you have when you log back on the next day.
There are some small bugs in the milbucks system, but it's not a big deal so I'm not going to/can't do anything about that.
The MilBucks are just a cool extra feature in the forum, and being allowed to post in such a cool/great/awesome (add your own words) forum should be reward enough...