The WYSIWYG (ckeditor) adds a paragraph tag <p></p> around the text within the block quote. This causes it to inherit the text size of your paragraph base style.
If you add a block quote via the WYSIWYG it will automatically apply a Paragraph tag around the text with your block quote tag.
This is actually semantically correct but it may cause unexpected results if you have styled your block quote text to be different to your base paragraph.
A simple solution is to add a child p selector to your block quote style and then apply your text styles to this also.
This way, if your block quote gets paragraph tags added within it, your block quote style will still display as expected.