Just yesterday I received email from London Visa office asking explanation letter why I went to Saudi Arabia and came back same day?
Actual story is I went for Umrah on my car, while coming back at saudi border they put exit stamp on my passport but that lazy immigration officer didn't bother to Exit me on his computer system. After few days my travel agent call me and asked me to again go to Saudi Arabia border and ask them to Exit you from their system otherwise you will be considered illegal resident in Saudi Arabia as in their system you're still in Saudi Arabia, so I made a visit to Saudi Border again for few minutes which cost me 12 hours of round trip from Dubai to Saudi border.
Anyways because there was a Exit and Entry Stamp from United Arab Emirates border (no saudi entry for that day) so now CIC needs an explanation of this visit. If there is an Exit Entry stamp on your passport, you need to mention it with little description. If they need any explanation they will send you email, but don't leave a gap of being rejected due to misrepresentation.