compound clips have different frame rate from source

I've just made a compound clip from two 59.94 fps clips and the resulting compound is 24 fps! The initial clips imported correctly at 59.94 fps. The project setting frame rate is 29.97 (nobody said anything about 24fps). Essentially this has tossed more than half my frames and my plans to playback the compound clip at 1/4 speed. Any guidance on what's going on here?

Many thanks

Bruce