I ran into this with my symtab lookup cache patch, PR 17799.

I think the problem can also be seen from ada, which has its own symbol lookup cache, except one will need to fix PR 17854 first (assuming I'm not missing something).

diff --git a/gdb/symfile.c b/gdb/symfile.c                                                                                                                       
index d55e361..ad481de 100644                                                                                                                                    
--- a/gdb/symfile.c                                                                                                                                              
+++ b/gdb/symfile.c                                                                                                                                              
@@ -3023,6 +3023,12 @@ clear_symtab_users (int add_flags)
   /* Someday, we should do better than this, by only blowing away                                                                                               
      the things that really need to be blown.  */                                                                                                               
                                                                                                                                                                 
+  /* Notify anyone listening that the previous loaded symtab(s) are invalid.                                                                                    
+     It is important to do this before calling breakpoint_re_set as the latter                                                                                  
+     will try to look up symbols, and for example the symbol cache needs to                                                                                     
+     be flushed first.  */                                                                                                                                      
+  observer_notify_new_objfile (NULL);                                                                                                                           
+                                                                                                                                                                
   /* Clear the "current" symtab first, because it is no longer valid.                                                                                           
      breakpoint_re_set may try to access the current symtab.  */                                                                                                
   clear_current_source_symtab_and_line ();                                                                                                                      
@@ -3032,7 +3038,6 @@ clear_symtab_users (int add_flags)
     breakpoint_re_set ();                                                                                                                                       
   clear_last_displayed_sal ();                                                                                                                                  
   clear_pc_function_cache ();                                                                                                                                   
-  observer_notify_new_objfile (NULL);                                                                                                                           
                                                                                                                                                                 
   /* Clear globals which might have pointed into a removed objfile.                                                                                             
      FIXME: It's not clear which of these are supposed to persist