I have a very little text (font-size="0.050") placed iside a zoomed box (<g transform="matrix(400.0 0.0 0.0 -500.0 -4666.6668 21900.0)"> ) the text is not rebdered, you can compare the rendering of other browsers (... not IE).
At the URL specified you can find a test case.
Seems like a bug. Enabling-disabling the "minimum font size" in Safari does not change the behavior here. We'll need to make a better/simpler reduction.
a simpler test case:
I hope this can help, it seems that the problem is in the calculated font size (too big). The font size is "0.05" and zoom factor is 100.
If font-size is 1 all works fine
The patch on bug 12448 fixes this problem. Thanks a lot for the testcase, I've integrated it in my patch.
*** This bug has been marked as a duplicate of bug 12448 ***