This problem occurs in a multinode environment, made of a NoMachine Enterprise Terminal Server (the main server) plus Terminal Server Node hosts (the nodes).
Clipboard settings can be ruled via the EnableClipboard key in the server configuration (server.cfg file). It should be possible to define different settings for each node. Setting the clipboard on the remote node doesn't overwrite settings in the main server's configuration.
As a possible workaround, comment the EnableClipboard key in the server.cfg file on the main server and on the remote nodes so that the default setting is used (copy and paste is enabled from local to remote and vice-versa).
Then set the clipboard behavior on per-node basis via server profile rules.
E.g.
1) Allow or disallow copy and paste from user's pc to server side
/etc/NX/nxserver --ruleadd --class feature --type client-clipboard --value yes --node <NODE>
/etc/NX/nxserver --ruleadd --class feature --type client-clipboard --value no --node <NODE>
<NODE> is the name of the node as it appears in the output of /etc/NX/nxserver --nodelist (in the format of name:port). It can be also the main server host, e.g. 'localhost:400'
2) Allow or disallow copy and paste from server side to user's pc
/etc/NX/nxserver --ruleadd --class feature --type server-clipboard --value yes --node <NODE>
/etc/NX/nxserver --ruleadd --class feature --type server-clipboard --value no --node <NODE>