I've noticed that before as well, though I sometimes don't do any training for like a week or so, I can still do the same amounts of reps with the same amount of weight, I actually feel stronger then...
Just to mention something as well, strength and power is generally one of the last things to go for the body, when you have stopped training for a while.
The reason why I say this, is that I have found that after I had taken a relaxed attitude to my sport, swimming, as I needed to focus more on my University, this meant that i reduced my training to almost once or twice a week. However, at this moment in time, I have not trained at all for three weeks.
However, bizarrely I am actually swimming faster in the last two weekend races that I have participated in! Well, they were short sprints....
Therefore the muscle memory for me in swimming is still there and I still have enough power and strength for me to still get good times out of myself.
Also, when I was reducing my training from nine sessions a week down to the five sessions a week, my performance had improved, as I was able to get more rest for the sprint based races, however the distance races had suffered....rather considerbly.
Therefore it generally depends what sport and what you want to get out of it, for weight training. For me, I am happy with myself. However I know that soon, to maintain the speed I will need to indulge in a little bit of vanity of weight training...

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Performance for skill based sports can suffer almost immediately when stopping training, however in the grand scheme of things (unless you're hardcore trainer and train night and day) it won't be noticeable.
Hope it helps,
Submerged