There have been recent reports of people missing their Visa page from their passports. There appears to be some sort of racket of tearing away the visa page while at the immigration or at the baggage area on the pretext of examining the passport.
Recently an UAE resident was unable to board his return flight to Abu Dhabi when he realised that his visa page was torn. There have been similar incidents in the past and specially with visa of USA, UK, and Europe.
So guard your passport, and keep it in sight at all times, and even if you have to hand over for an extended period, then check that all pages are intact.
Read more here: Emirates 24/7