If you bought shares of China Banking Corporation (CHIB), at around 390-400, you might be tempted to sell now since the it's trending down.
But if you do your math, you can still put your stop loss for CHIB at around 348 per share. Since there's a PHP12 cash dividends and 10% stock dividends, thus at 348-360 per share of CHIB is still breakeven.
Further, my opinion is that there are motivated sellers out there, trying to pull down CHIB prices so that they can get in at around 400 per share. Further, based from the charts, CHIB prices does not react violently at EX-DIV date.
S - Stock Split (Stock Dividends)
D - Cash Dividends
Based from the chart above, after the ex-div date, there is a slight decline for CHIB, you have all the time to decide what to do then. No need to panic sell now, even if the price per share drops to 400.