TinyMCE is part of WordPress and it comes with own styles. GD bbPress Toolbox Pro loads an additional stylesheet for TinyMCE to solve common issues when TinyMCE is used on front end. But, depending on your theme that might not be enough. Some themes are adding very aggressive styling that targets elements in TinyMCE too (usually buttons), and these theme styles are causing problems.
The only solution is to find what styles theme is adding to cause the problems, and add extra styles to fix that, but that has to be done for every theme individually. Most themes are using proper styling that is not causing problems.