Hi, I wondered when it was you pruned the acer? Its possible you have pruned it at the wrong time,the best time being in its dorment months,however its better not bind it with anything as the air is best for healing the cuts. I do mine between November and february and they seem ok. :)

Thank you for your advice, I did prune it recently during a warm spell. I will keep an eye on it and with luck it will live through my impromptu pruning!
Cheers

Which particular Acer are you referring to>

Unfortunately, this year, the sap was up early - Acers should be pruned, if necessary, after July and not after January.