org.openxmlformats.schemas.spreadsheetml.x2006.main.impl.CTXfImpl instances kept increasing each time the spreadsheet page is refreshed (esp. in Chrome) or styles are applied to the cells.

Steps to reproduce:
1. Use Java VisualVM to sample memory
2. Observe the instances of CTXfImpl (via filter)
3. Perform the following operations in any sequence:
a. refresh page
b. select a range of cells and apply some styles

• bold/underline/italic (reused; constant increase)
• border
• foreground/backgrounnd color (not reused; increased proportional to number of cells)