My question is whether the solicitor can do whatever they like without informing me (the client) or do as they see fit and beneficial to the agent? Or is it a standard thingy?

1) Check whether the lawyer is acting for you or acting for purchaser because normally agent will get "common solicitors" and this "common solicitors" actually acting for purchaser and not seller. If the lawyer is really acting for purchaser, kudos, the lawyer technically doesn't owe you any obligation. You can slap yourself for trusting the agent too much. If the lawyer is acting for you (as seller) then they cannot act without informing you unless it's matter of immediate action (ie matter of life and death).

If there is a problem here, where can I bring this matter to? To me is the matter of principle.

2) Well, the answer is similar to the above. Your principle is worthless if the lawyer is acting for purchaser as you have opted not to be represented in the sale and purchase transaction. If the lawyer is acting for you, you can always lodge your unsatisfactory grievance with bar council. Sila rujuk kepada pak cik google untuk maklumat lanjut.