act up

Reader's Digest 1月号の@WORK (Tales from the office water cooler) コーナーの投書から引用します。
The computer in my high school classroom was acting up. After watching me struggle with it, a student exclaimed that my hard drive had crashed. So I called IT for help.
"Can someone look at my computer?" I asked. "The hard drive has crashed."
"We can't just send people down on your say-so," said the specialist impatiently.
"How do you know that's the problem?"
"A student told me," I said.
His next reply was swift. "We'll send someone right over, Sir."
今時の生徒の方が先生よりもコンピュータに詳しいと言う事なのでしょう。
最初の文に出てきた "acting up" は文脈からして、「（コンピュータの）動きがオカシイ 」の意味だと推測できますが、"act up" がその様な意味を持つことは意外に思えます。辞書で確認します。
・Merriam-Webster's Online Dictionary: to function improperly: this typewriter is acting up again
・Macmillan Dictionary: if a part of your body or a piece of equipment acts up, it starts to become painful or to develop problems: I hope my back doesn’t start acting up again.
・Cambridge Dictionaries Online:
* If a person, especially a child, acts up, they behave badly: Sophie got bored and started acting up.
* If a machine or part of the body acts up, it does not perform as well as it should: My car always acts up in cold weather.; Her shoulder was acting up (= hurting because of injury).
装置だけではなく、身体の部分、人（子供）も "act up" する事があるのですね。
後半に出てきた "say-so" も面白い表現なので明日取り上げます。