i would wonder whether you are getting some enolisation of your aldehyde under those conditions, followed by allsorts of nasty side reactions (aldehyde aldehyde aldol etc). Has anyone used some more reasonable conditions? (ie. for an ester-aldehyde condensation i'm doing, i cool LDA/THF down to -78 degC (1.3 eq dry diisopropylamine and 1.2 eq titrated BuLi), add 1.4 eq ester, stir at -78, add 1 eq aldehyde, stir 1 hr at -78, quench with NH4Cl and workup). I would give these conditions (or similar reported ones) a go.