tlscd, page-2

In theory Ex and cum produce identical returns- i.e. when a stock goes Ex divvy it falls by the value of the dividend. But then that is the ideal / efficient market behaviour - which does not take into account dividend preferences.

The key downside risk is this: Telstra is a yield stock whose shareholders strongly prefer dividends to capital gains. Telstra has additionally run up well to the Ex date ($2.55 to $3.40). It is likely that a large number of fundies are hanging on to take the divvy and then sell at a capital gain. That would cause Telstra to fall by more than the divvy. [i.e. it is probably a good idea to sell now or be exposed to a short term loss - but over the long term TLS is a BUY!]

Since those same fundies prefer dividends they are likely to jump back in at some point probably in 3 to 4 months to build a stake prior to the next dividend.

The winning strategy could be to be contrarian, avoid the dividends and buy Telstra Ex Div. Doing so MAY get you Telstra a point or so cheaper due to dividend preferences driving valuation, but then dividend preference arbitrage is closely watched and priced out.