Are you accidentally sliding down on the options/settings tab (fifth one over. looks like a gear right above the "i")? Sliding up or down on that will reduce or enlarge the keyboard. I know I've done it sometimes by mistake when typing too fast. Touching and sliding up on that to restore the keyboard to a larger size.
Quote:
Slide UP or DOWN on the Option tab to resize the keyboard. 
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http://www.cootek.com/V3Help/TouchPal3Manual.htm