SUMMARY
Users with non US English regional settings, editing a Report Services Document using Strategy Web 10.3 encounter an issue leading to gigantic fonts after making a modification of the textbox font property.
1. Set Web user preferences > General > Language > Number and Date format to a non English (US) locale, e.g. Spanish (Spain).
2. Create a new report services document and insert a textbox

3. Right-click the textbox and choose "properties and formatting". Change the font size under Format > Font.

4. Execute the document
5. Return to Edit mode and make a modification to the textbox font size again.
6. Run the document again and notice the gigantic textbox and content.

CAUSE
This is a known issue with Strategy Web 10.3.
ACTION
This issue has been addressed with Strategy Web 10.4. Upgrade to take advantage of the fix.
WORKAROUND
1. Change Number and Date formatting settings to English US and the issue will not occur.

2. Use Strategy Developer to modify the font size.