Cannot change size of a paragraph text frame, if text frame is turned by 90 or 270 degrees

Hi, I encountered a problem: I converted a DXF file to a Corel Designer file. This DXF file also has some dimensions which turned into paragraph text. This paragraph text is turned by 90 degrees. The font size is rather small, so I increased it by some points. As the paragraph text frames were now too small, I tried to increase their size. However, the text frames always jump back to their original size. I experimented a little bit and noticed that this is only, if the text is turned by 90 or 270 degrees. If the text frame is not turned or turned by 180 degrees, you can change the size of the text frame. Additionally this problem arises only, if the option "Expand and shrink paragraph text frames to fit text" is activated (in Tools | Options | Workspace | Text). Sometimes some text frames were adapted automatically, when I changed this option. However, I do not know when which text frame was changed. Is this a bug? Or did I miss anything? Corel Designer X6, service pack 1 Best regards Winfried