I'm not sure, I've never been stuck in a community room before. In steempeak the default when making a post is in My Blog,
The drop down by MY Blog lets you pick which community you want, but with recent upgrades in may have stayed on your previous choice.
If it stayed on previous choice just click MY Blog and that should fix it. I have no idea how it works in steemit any more.
Thanks @bashadow. I'm still using steemit.com, probably the least intuitive interface available. The only way to find communities is convoluted and quite the treasure-hunt. Team Steem really needs someone on their team that has skills in creating a good user interface .