It still works the same. There are two issues here:
1: Select the text layer you want to edit.
2: After selecting the text tool, make sure you place the cursor on the
line of text you want to edit before clicking to place the cursor in,
or behind the text on the line, or selecting the block of text with the
text tool cursor. If not, CS5 will function as if you want to add
another text layer.
So, just be aware of where you place that text cursor before making the
edit selection.
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Regards,
Savageduck