in reply to Re^2: How to run perl5.21.3 as "perl"
in thread How to run perl5.21.3 as "perl"

To clear the cache, enter "hash -r".

Ok - sounds like that must have been the problem.
Odd that it hasn't bitten me before - but this is the first fix I'll try if it recurs.

Acknowledgements to aitap, oiskuu and ikegami for raising/pressing this point.