bug#28645: 26.0.50; semantic-ia-fast-jump jumps to a random place in buffer

[Constantine]

When declaration is in another buffer, semantic-ia-fast-jump often
jumps to this buffer, but to incorrect line. However if the
declaration is in the same buffer where the command was used, it always
— as far as I've seen — jumps to the correct line.

Steps to reproduce:

1. Create the following 2 files with the following content:
    $ grep -n "" myfunc.h test.cpp
    myfunc.h:1:void myfunc1() {
    myfunc.h:2:}
    myfunc.h:3:void myfunc2() {
    myfunc.h:4:}
    test.cpp:1:#include "myfunc.h"
    test.cpp:2:
    test.cpp:3:int main() {
    test.cpp:4:     myfunc1();
    test.cpp:5:     myfunc2();
    test.cpp:6:}
2. Run emacs -Q test.cpp
3. Enable `M-x semantic-mode`
4. Put cursor into "myfunc2", and type `M-x semantic-ia-fast-jump`
    (you'll see it jumped to the correct declaration at myfunc.h file)
5. Use `C-x b RET` to switch back to test.cpp
6. Put cursor into "myfunc1", and type `M-x semantic-ia-fast-jump`

Result: it jumped to "myfunc2" declaration, not to "myfunc1" as it ought to.

I also want to note that though ATM I am using emacs-git, I've seen the
problem for don't remember how long, just didn't report.