Need some answers if possible about pinball slots.

I was at the Beau Rivage in Biloxi this week and used my free play on a $5 Pinball slot. My approach was to bet once credit...two credit...two credits, etc. until I exhausted the free play. The Beau requires you to put some real money in to activate the free play . I put in $5 cash and began the sequence. Tapping the one credit button once and then twice and so on. Well when I hit the button for the fourth time spin (two credits) I got the bonus feature that should have been 4 tries of the pinball. Instead I only had one!!! Imagine my shock when I expected a big win but got a much smaller one.

My question is --Does the initial cash input limit the number of credits you can bet? I tried the max credit button after this happened and still it only registered one credit.

Did recover $150 bucks on $100 free play but I was sure I had much more.