hg grep seems not very effective to find strings of old changesets!?

[Uwe Brauer]

Hello

Maybe I don't know enough of the sophisticated syntax of «hg grep» but I
have always found hg grep not very useful.

Here is an example: I have around 700 change sets in a current repository 

I found out that in revision 562, the string   \label{eq:section4-sh15}
appeared in a certain file. However hg grep was enable to find that
string in that particular revision.

Is this a well known limitation of hg grep or do I miss here something
fundamental?

Regards

Uwe Brauer