I was helping my son on an A-level (high-school) physics problem. 
I entered 4 then "x10y" then -20 then / then 2 then "x10y" then 14.

That is I wanted to calculate 4e-20/2e14  and was expecting the result 2e-34.
what was obtained was 2e-6.  

The problem is the "x10y" button inserts a "times 10 to the" into the calculation. The problem is essentially a one of operator precedence. 
The intuitive expectation (and the behaviour of most other scientific/engineering calculators) is that the "x10y" is applied firstly to the preceding 'mantissa' before the rest of the calculation. This operator binding should be as, or nearly as, strong as a ()s.