I checked again and it's not the sensitivity , it's the pulse duration , bellow 5% is accurate only up to 10KHz .
But as I said at 3,3Vpp it is not accurate at all at high frequency , again only to about 10KHz , at 100KHz the error is very big if the duty cycle is <50% or >50% .
At 5V logic it is very accurate at 100KHz , maybe 0,2% off , like in specs for 5%-100%.
I don't want to say that is bad or out of specs , it is how it is , personally I don't care too much . For 5V logic circuits it is very OK . But people should know its limitations .