Add .gdb_index and CRC mismatch

For the remote debugging and local copies of shared libraries, should .so CRC be affected by
adding .gdb_index as described at https://sourceware.org/gdb/onlinedocs/gdb/Index-Files.html?
After adding .gdb_index, 'target extended-remote :XXXX' refuses to load local copy with
the following message:

warning: the debug information found in "/xxx/yyy/lib/debug/libzzz.so" does not match "target:/lib/libzzz.so" (CRC mismatch).

If CRC was actually changed, how is it indented to use .gdb_index for the remote debugging?
And why there is no CRC warning when I do 'add-symbol-file /xxx/yyy/lib/debug/libzzz.so [addr]' manually?

Dmitry