neither importing the PSD as ‘composition’ or ‘composition – cropped layers’ made any difference. however your suggestion of making the comp size bigger worked.
my AE project was DV/PAL [720×576] but the imported PSD file was being converted by AE into a composition the same size as the original PSD file. when i adjusted the ‘composition settings’ to make this composition also 720×576 it started behaving as expected.
funny! – i can never remember adjusting the comp size when i’ve done this before. perhaps i’ve just forgotten doing it – or is there a pref somewhere that i may have had set previously, which will automatically create all new comps at the same size as the main project?
thanks for your help, folks.