"Je le mets sur l'étagère."

Translation: I am putting it on the shelf.

[TraceyVP]

"I put it on the shelf" was rejected. Perhaps because first-person present and past tenses of "put" are the same spelling?

[Trofaste]

More through oversight. Added it now, because while it could be interpreted as past tense it's certainly a correct translation. The sentence for translation from English to French will remain "I am putting", of course.

[Ripcurlgirl]

That seems like a likely reason.