Things like this will happen occasionally because hotel employees are human. Humans make mistakes.

As catocony states, propping doors open is standard practice. I'll even go so far as to say that it's a very good thing. I've yet to stay in a hotel where guest room doors close without making noise. Just imagine the racket the housekeeping would make if they had to open/close guest room doors multiple times during the cleaning process.

My advice is to sleep on it. Maybe even go about your day tomorrow, as planned. If you still feel strongly about the problem, ask to speak to a manager to discuss it.