If we have port A low and we pulse the port B a second time during the discharge of the external capacitor, the output pulse is either shorter than expected, or worse just a single very short pulse! We would expect that the second pulse would be ignored (as it is with HEF4528 and stated in your datasheet). We have an RC of 1nF capacitor and 1.5k resistor. As you may see on the fist attached picture (ptm1), we have the second pulse ignored if it arrives after the full discharge of the capacitor. On the second picture (ptm2), we have the second pulse during the discharge of the capacitor, which reduces the length of the output pulse. On picture three (ptm3) it is even worse, because the output pulse length is the difference between the two input pulses. (note : blue trace is input on pin B, purple trace is capacitor on RX/CX pin, green trace is output Q) If a third pulse arrives, it retriggers the monostable!!! Strange situation for a NON-retriggerable monostable. Please note that the input pulses width (~20ns) are larger than the ones specified in your datasheet (min 5ns). In your datasheet it is written: "Once triggered, the outputs are independent of further transitions of the A and B inputs and are a function of the timing components". It is clearly not the case! Our "clear" input is still and not noisy, so it cannot come from this source. Do you have an idea on how to overcome this?