Hi Radim,

Sometimes the current parent style cascades better when defining the class for the style, e.g. try:
m_impl->m_terminalDisplay->setStyleSheet( "TerminalDisplay { font-size: 10pt; font-family: Monospace; }" );

to see if it gets rid of the side effects. Just guessing here, though, since I don't use the GRASS plugin's terminal on this machine.