[KS] Japanese and Korean yen in Korea?

[Bill Streifer]

On August 29, 1945, a B-29 Superfortress "Hog Wild" was shot down by Soviet Yak fighters over Konan, Korea while attempting to deliver food and medical supplies to hundreds of Allied prisoners at a (former) Japanese POW Camp there. By then, the Russians had taken away the Japanese guards. 
All 13 American airmen survived the crash, and they spent the next two weeks or so with POWs until a rescue plane was sent to fly them home. The POWs left Konan by train....
In the pocket of an officer of the downed B-29 crew was a Japanese note. Can anyone explain whether Japanese notes (in yen) or Korean notes (in yen) were more common at the time, and why both were needed (if, in fact, both existed at the same time in Konan). 
I've attached two photos:
1. The actual 50 sen Japanese note that was brought back from Konan as a souvenier.
2. A colorized photo of Konan taken during the POW rescue. At the left you can see the roofs of the POW camp and in the distance, the Chosen Nitrogen Fertilizer Complex.
Bill Streiferauthor of The Flight of the Hog Wild 
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