An equity investment should be classified as held for sale if it is expected to be sold within one year from date of purchase. However if the company is unable to sale it due to decrease in its market value (selling at price which will result in loss), the company can still contiunue to classify this investment as held for trading. If we pay close attention to wording of IAS-39 it say "Expected" to sold and not "Must" be sold.Therefore a company can continue to classify its investment as held for trading if it is unable to sell it in time.
Another example which explains this situation is where Company has as portfolio of investments in equity securities and trade them regularly however any one or few securities are not traded due to any reasons mentioned above. In this situation company may continue classifiying its investments as held for trading.