It's to separate the abbreviation from the grammatical suffix.
laid is the simple past tense and past participle of lay, which is the active verb which means 'to put' something, this is what a person does to produce the result that the keys lay or were lying on the TV, those two are the correct English forms in this case.
lay is not only the infinitive of the active verb, it is also the simple past of the stative verb lie as in 'to rest in a horizontal position' – it's pretty confusing.
While this is absolutely correct, most Americans (I can't speak for other English speakers) honestly don't understand this distinction, and wouldn't consider "laid" to be wrong (even though it is). In fact, a good number of them would think "lay" is wrong.
I'm usually more inclined to descriptive than prescriptive rules, but in this particular case I simply can't accept the misuse, mainly because all other Germanic languages have a clear distinction (and we English learners tried to hard to wrap our heads around it too)
I wrote "Nycklarna låg på teven" but it didn't like "teven". Is there a difference between "teven" and "tv:n"?
teven is a little more casual but both are perfectly OK. It's just that the dictation exercises don't accept any kind of spelling variation. It's been reported as a bug but it probably won't be fixed any time soon. It's accepted when translating though.