While usually the profit made and the change in NAV should be in the same direction, there are special situations where this is not the case. 

Here is one of them: 

This special case is always linked to (substantial) inflows or outflows that alter the Net Worth (NW) of the user.

Take this example:

Period 1: User has ~1m in NW and makes a loss of 10'000 which is -1% in performance 

i.e. NAV is 99 at the end of the period.

Period 2: User has inflows of ~1m and now the total NW is ~2m, user makes a gain of 15'000. 

That is only 0.75% on his 2m capital so the NAV will go to ~99.75 (there is rounding here, ignored for the purpose of the example). 

When we chose to look at Period 1 and 2 together we will now find that performance is + 5'000 (being -10'000 and + 15'000) but the % number is negative 0.25% (being 99.75 [ending value] - 100 [starting value])