Market-to-Market profit or loss. Is it error in broker system?

Dear Friends,

What i observered have created a fear for re-entering a position of same stock even after square-off.

This is what i saw:

I purchased futures of ABC company at price suppose: 200/-
Price rose to 250/- and yet to square off, when it shows me MTM profit as 50/-

I square off and get a nice 50 bucks profit.

Now starts the drama !!!
The price fell to 100/- and starts rising from there.
I re-purchase the shares at 100/- but here it shows me, i have a MTM loss of 100 Rs !!! As the shares value now starts increasing from 100/- my loss reduces.

I am utterly confused. I did squared off in the first transaction, then why does the system compare with the earlier price??

Pardon me, if i missing something, and again beg an apology in advance. But please help me to understand this !!

Thank You once again.
EDIT:
Additionally the quantities purchased before and after are added as well.

Can someone kindly answer me on this?

I experimented and this happened today as well. I was short on TataSteel Futures, and as soon as i got long (when prices increased after reaching rock bottom), it gave me a M2M loss.

which broker you are using?

Sharekhan is my broker, and this i have observed only in futures. Equity works as expected.

plz explain this...!!!