LT6650 input/output oscillations

Hi to everyone,

I'm sorry if the question could seems trivial to someone, I'm an electronic engineering student and I'm trying to use the LT6650 as voltage reference (>450mV) for a comparator input.

I've tried the basic configuration shown in Figure. 8 at page 9th of the datasheet and it works very well, then after a deep reading I've tried to modify the input's RC filter and the output's load capacitance to better suite a noisy environment as explained at page 8th. 

First try:

1) Input RC filter changed as shown in Figure. 2, output capacitance at 1 uF as reference:

The result is that during the output's settling time the OUT pin of the IC sinks a current with a maximum of about 9 mA resulting in an output's voltage undershoot that is recovered in about 3 ms.

2) RC input's filter as 1) and output capacitance changed to 10 uF:

The current in the output capacitance behave as shown in the figure.

3) Input filter as in reference Figure 8 (1 k - 1 uF) and output capacitance increased to 20 uF:

The current in the output capacitance oscillate.  The problem could be resolved increasing the feedback capacitor, it's sufficient 2 nF to make the oscillation disappear.

Is there anyone who can explain me why the circuit behave like that? Is it wrong changing the feedback capacitor? Is it possible to avoid the strange output capacitor's current behaviour when increasing the RC time constant of the input filter? (Case 2) Thank you to everyone.

PS: the circuit topology is as follow: