LTspice default rising/falling times of pulse edges

Above is how I set up a pulse in LTspice.

When I set the rising and falling edges as zero or if I do not register any value, in that case LTspice automatically sets the rising and falling edge duration. In above case it is 25ms for a 2Hz pulse. So if I want a very sharp pulse I have to each time type something like 0.0000001 instead of 0.

Can there be a reason for this default settings or is this a bug?

Answer

is this a bug?

No.

Can there be a reason for this default settings

Yes. This is explained in this FAQ on the LTwiki website:

I have a pulse source in my schematic with zero transition times. LTspice only shows slow transition times of 2ns. What's going on here?

It explains:

LTspice automatically will use a default value for and if these parameters are set to zero. Default value: 10% of Ton or 10% of Tperiod-Ton whatever is smaller. You must specify Trise and Tfall if you want a certain value.