The past couple of times I've been in the gym I've done some workouts that specifically called for an exercise rep to failure as the last exercise of the routine. For instance finish with decline pushups 3 sets to failure and today weighted dips 3 sets to failure.

I noticed on both workouts that the first set I failed at say 25 reps, then the 2nd set I crapped out at like 30 reps, then the 3rd at like 22.

Same thing happened with the dips today. Anyone know why this happens?

Logically I would think as I progressed through the sets I would be able to do less reps, not more. Of course I have found little "logical" with my body!

Did you warm up properly before starting? That could be it.

Both exercises were at the end of body area-specific sessions so I would assume that the affected muscles were appropriately warmed up.

For instance, the first time it was an upper-chest specific routine:

Incline Smith Press 4 X 6/10/12/15
Incline DB Press 3 X 10
Incline DB Flye 3 X 8/10/12
Decline Pushups 3 X Failure -- it was here where I got 25 reps, then 30, then 22

I was actually kind of laughing on the second set wondering why I could keep cranking them out on that one but not the one before. I would have expected to go 30, 25, 22 or something like that with progressively decreasing reps. I chalked it up to a fluke until today when the same thing happened with another exercise.

Perhaps since you were tired from the first set, you did not pay attention to proper form for the second. Improper form can easily allow you to do more than with strict form since you are going to be easing up on the tired muscles and allowing other muscles to take some burden that they shouldn't be taking.

Or, another theory, is the first set to failure set off a flood of adrenaline and endorphins, allowing you to push farther the second set. From experience, I must say this really does happen when you push hard and it lets you push a lot farther than you ever thought. The laughing by the second set because you were going so hard really makes me think of the rush; that's the endorphins doing their thing.

If you know you kept good form, then the second theory is likely what happened in my opinion. Of course by the third set no amount of hormones would help your dead muscles.

was the amount of rest identical between the sets?

honestly it just depends. did you watch the olympics? did you notice in the relay runs, or the long swimming competitions...some athletes hit it hard early, then held onto their lead...other athletes started off slower, than exploded with speed late in the match?

different people hit their stride/peak at different times under different conditions.

not to mention the previous 36 hours food intake's influence on this training session, the previous nights amount of sleep, and supplementation such as creatine all are variables in your scenario.

yoru first set to failure really pushed you hard. the second set, you went further...and on the third set you were truly spent.

one could interpret this as 'you're not pushing yourself as hard as you could, but you did on set #2'...and that's entirely possible.
however one goal behind training to failure occasionally, is to push through roadblocks. That may be exactly what you did here.

I wouldn't over-analyze this too much unless it becomes a consistent, repeatable event.
even then, if you are making gains and getting stronger, why question your success? relish in it!