Matlab: using a small sample time for sine wave, makes the wave's frequency "accelerate"

Question

I noticed that if I use a small sample time of DSP sine wave in matlab, the signal's frequency "accelerates":

This is the signal with a proper sample time:

But if I reduce the sample time too much:

And the effect remains for even lower sample rates:

Any idea why this is happening? It must be a simulation bug right?

And, how can I fix it? I guess messing around with solver settings will get it right, since the issue has to do with sampling. My current settings are:

Answer 1

Any idea why this is happening?'

Aliasing

how can I fix it?

Always use a sample rate above the Nyquist rate for the frequencies contained in your signal. Preferably by at least a small multiple (called oversampling)

Note: The title of your question is misleading. The problem didn't occur when you made the sampling interval too small. It happened when you made the sampling interval too large (and so the sampling rate or frequency became too small).