We can provide a very simple C reproducible test case if that an save you time

please, do! You can attach it to the issue.

Hi Stephane,

Here is what I'm getting with the provided test:

$ ./mdev-4075
One:Exec OK
One:Fetch OK 1

$ ldd ./mdev-4075
linux-vdso.so.1 => (0x00007fff795ff000)
libmysqlclient.so.16 => /usr/lib/libmysqlclient.so.16 (0x00007f923856e000)
libstdc+.so.6 => /usr/lib/x86_64-linux-gnu/libstdc+.so.6 (0x00007f9238267000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f9237fe2000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f9237dcc000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9237a29000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f923780b000)
libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f92375f3000)
/lib64/ld-linux-x86-64.so.2 (0x00007f9238989000)

General log contents:

7 Prepare SELECT 1 FROM DUAL WHERE UPPER(LEFT('emstoto',3))=UPPER(LEFT(?,3))
7 Execute SELECT 1 FROM DUAL WHERE UPPER(LEFT('emstoto',3))=UPPER(LEFT('ems',3))

So, it looks like everything works as expected. Same with libmysqlclient-18.

Could you please provide the same from your test runs? Test output, ldd, general log.

Thank you.

Hi Stephane,

You were going to get more information on this, any luck?

Since there is no new information on the issue, I will close it for now. Please re-open (or comment so we could re-open it) if you have any news.
Thanks.