After further investigation, I realized that this problem only occurs in the Chrome browser.
But the previous fonts that I made with G2 do not have this problem in Chrome.
I sent the font file with a sample text of this problem.
It seems to have to do with kerning with the space glyph. If you remove that, the jumping around stops. I don’t know whats actually happening but it seems to be a but in Chrome as it is OK every else.