RHEL8 system gdb currently ships gdb-8.2. The bug discussed here was introduced
with the source highlighting feature introduced in gdb-8.3. Moving this to DTS9.
This is addressed in GTS10 already [it is part of FSF GDB 9.2 release]:
2019-10-24 H.J. Lu <hongjiu.lu>
PR gdb/25126
* symfile.c (reread_symbols): Call forget_cached_source_info to
clear the stale source cache.
The test from Sergio is missing, but it is (obviously) not needed.
Closing.