Peshwa,
In this country you need to know your right and without it
you may end up in bad situation.
Take an example.
How do you know that they filed for I-485 already?
I understand they indeed did, but they have to show
you the proof (and that's the receipt number).
Assume they didn't file it and your visa expired.
That means you are without status. Now employing
a without status person, the company may be panalized.
But for their case it's a question of only money. And in your
case you may be deported or you have to explain your
without status problem as long as you live in this
country.
Secondly, any immigration/visa related things, it's
not just employer's ball game. As long as you are involved,
the whole "ball game" has to be transparent for
all three sides - the lawyer, the employer, the employee.
There is no hide and seek here.
Thirdly, after six months your pending I-485 is portable.
That means you can join another company and carry
the I-485 to to new employer. In this case, your current
company is "liable" to provide the receipt number.
They cannot deny it.