Hello bramble,
We are not aware of any issues with changing the font size within the description editor so it is not clear what may be occurring for you. If you have already tried clearing the cache of your browser and the difficulty has persisted, please feel free to file a support case letting us know the details of what you have tried and what is occurring so we can take a look into it. Please include your operating system and browser information in the support case and if you have encountered an error message, please include the full text of that message in the case and we'll be happy to take a look.
- Craig