Please refer to the git repository of htop, the bug is https://github.com/hishamhm/htop/issues/882
In InfoScreen.c file, there is a potential use of uninitialised variable bug. In Line 133, it calls the function getmouse(&mevent) and mevent may be uninitialised after the function return. As we can see below, the library function getmouse would return ERR without initialising its parameter aevent (when the path condition at Line 1761-1764 is false, it will directly return ERR and not initialise aevent). Then, in the file InfoScreen.c, at Line 133, the path condition is false, and the Line 133-136 will not be executed. However, the Line 137, "if (mevent.y == LINES - 1)" will be executed, and mevent.y is not initialised at all. I guess there is a missing "else" in Line 137, which is the root cause of this bug.
Thanks for opening the upstream issue as well, it is sad that no one there is replying or merging your change as the preferred way would be to grab a new version of it.