How does the ARM Compiler (Version 5) handle double-precision floats in devices whose floating-point unit hardware only supports single precision?
and it appears that the FPU-specific instructions are being used! 


That is indeed correct. You have both load and store instructions available on the single precisition FPUs, but none of the actual calculation instructions.

Note that this may make some software calculations using double slower, as function arguments will reside in the FPU but must be transferred back to CPU registers in order to actually use them.