It's an unfortunate side-effect of being given a sentence with no context. If I walked up to you shivering and said jIbIrqu', you'd understand that I mean I'm very cold right now. But if I were telling you a story about how I once went skinny-dipping in the winter and I said jIbIrqu', you'd understand that I mean that I was very cold at that time, not now. Klingon does not mark verbs for tense; it indicates time contexts in other ways.
In Duolingo, you get no contexts with the sentences, so there's no way to confidently translate into a particular English tense. jIbIrqu' could mean I was very cold or I am very cold or I will be very cold depending on the context. To get around this problem, Duolingo lets you choose any of those possibilities.
A fairly good explanation is given in the Tips & Notes. If you have not been reading the Tips & Notes, I would like to ask that you review those so we don’t have to continuously repeat the information that we have explained there. If you have read them and still have a question, please be specific in your question so we can figure out where the confusion is.
If you are doing the course on iOS or Android, you cannot currently access the Tips & Notes through the app. To access the Tips & Notes, you will have to access the course using a web browser at https://www.duolingo.com/, either from your mobile device or from a computer. When you click on a Skill, it will expand to reveal a Start button and a light bulb.
If you click on the light bulb it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
The extra details are very helpful in answering your question, though I'm still not sure what went wrong. This particular sentence is set to accept past, present, and future. Did you report it as "my sentence should be accepted"? I don't see any reports. Did you happen to take a screen cap I could look at?
No problem. Only "My sentence should have accepted" is a valuable report. We get to see what you wrote and can compare it to the alternatives we have. All the other reports basically just say, "something's wrong here" with out any indication what it is. So coming here is a great way to communicate specific problems to us. But the more details and specifics we can get the easier it is for us to find the problem.