There's definitely a client difference here. When smbclient connects, it makes a single OpenAndX request; the kernel cifs client instead calls NTCreateAndX, followed by two SET_PATH_INFO Trans2 requests. The SET_PATH_INFO is probably what's clobbering the ACL.
Partial network trace showing the cifs client requests attached.
There's definitely a client difference here. When smbclient connects, it makes a single OpenAndX request; the kernel cifs client instead calls NTCreateAndX, followed by two SET_PATH_INFO Trans2 requests. The SET_PATH_INFO is probably what's clobbering the ACL.
Partial network trace showing the cifs client requests attached.