I'm currently on a summer internship while being in a unpaid leave at my regular work. What is the most succinct way to denote this on my CV so that I don't get misunderstood I'm doing the two jobs at once? Should I put everything describing my regular job in past tense?
Create an INTERNSHIP section
Name of Sponsor (Summer 2014)
Joined internship while on leave from my permanent position at ACME. As intern, developed ... [list your activities]...
Write up your permanent position as if you never took a leave - Yes, you took a leave, but even as you were doing the internship, the permanent position was still yours i.e. you never quit your job.
If you didn't learn or do anything worthwhile at your internship, you have the option of not mentioning that internship. In this case, you'll spill the beans about the internship only if somebody asks.