a flaw in tactics trainer

I like tactics trainer it is one of the reasons why I am a Premium member. However one thing bothers me.
tactics are rated on how many solves them and how long it takes to solve a tactic.
that's all fine but if I get a tactic and I can't solve it and get -1 and I decide to study it in order to understand why I did not solve it. I might suddenly understand it.
I click next and suddenly the same puzzle I couldn't solve appear and can now solved it within 0:02 seconds. it is just a madder how fast I can move the mouse. even if I get the tactic 10 tactics later it is easy to remember. 
Now this tactic is kind of destroyed since everyone is expected to solve it within 2 seconds. the rating puzzle also get lower rating since I could solve it now.  if a lot are doing the same then some hard tactics might be expected to solved faster and are rated fare too low.
I think tactics that I have already tried to solve should start at 1 minute not at 0:00. it shouldn't be possible to get 100%.

Simply prevent a member from repeating a tactic?

Or do you use tactics trainer often enough to prevent this from being effective?