Bug with \vec{F}

[uvi1]

The sign above the letter F is not an arrow. It looks like ~.

[xarthurx]

I don't have the issue. It might be because of your font settings.

[uvi1]

I want to use Font "Computer Modern Sans Serif". When I use "Computer Modern" the problem disappears.

A solution may be: "\vec{\sf F}"

[s1291]

I believe this happens because you're using a sans serif font such as "Computer Modern Sans Serif", or "Helvetica".

As a workaround, you can include the package esvect and redefine \vec to be \vv: