Dear Miguel,
I am not aware of this problem, you are the first reporting this issue. It is a while, since OpenACS 5.10.0 was released (more than 3 years ago), and the changes between OpenACS 5.10.0 and 5.10.1 were quite substantial, so it is not easy to track the origin. Can it be that you are using a seasoned version of Tcl or NaviServer?
My first reaction is to switch to recent versions of OpenACS, Tcl 8.6 and NaviServer, and the problem will be gone.
all the best
-g