tetex-latex-1.0.7-67.7 with tetex-fonts-1.0.7-67.7 Run "latex file.tex" and check the generated "file.dvi". It will show a vector sign as expected on the first and all lines, but a "ã" (a + tilde) in the middle line.
Created attachment 117650 [details] file.tex
Created attachment 117651 [details] Screenshot-file.dvi.png
I receive a sane output when I don't use amsmath.sty. The bug is probably there.
Reported upstream: http://thread.gmane.org/gmane.comp.tex.tetex.general/951
Reported this to LaTeX upstream as well. I'll add a reference as soon as I'll receive confirmation email from LaTeX people.
The bug is now registered under codename amslatex/3812 and I got this reply: this is a known problem, and has been reported before to latex-bugs: - 3416: Amsmath's \mathsf \vec prints a tilde accent - 3683: Wrong output of \vec in supscripts we plan to deal with these all at once, and will do so under #3416. for this reason, we will close #3812. however, i've posted a request to keep you informed when a fix is made. we do not yet have a solution; a workaround is to create explicit commands to produce the vector in the proper font, for example: \newcommand{\romvec}[1]{\text{$\vec{\mathrm#1}$}} \newcommand{\boldvec}[1]{\text{\boldmath$\vec{\mathbf#1}$}} Barbara Beeton Technical Support