The flowering maple (not a true maple) may drop its buds due to insufficient light--or too much sun.
When first put out of doors, the temperature change may cause such drop. It should be given casual changes--out for a short stay, brought back in, out for longer stays until well adapted.
The amount of sunlight at either place--in or out--may be too much or too little when the change takes place.
Improper watering or maybe fertilized at the wrong time or in the wrong amounts may bring on bud drop as well.

Changing the individual cause might show a change for the good.

Thank you Jeannie for the bud drop advice. I have just repotted both my abutilons and they are looking very healthy and have produced masses of buds - BUT - some of them are still dropping off. You mention both watering and fertilizing but didn't tell me when/how! As I inherited both these plants from someone I know very little about these plants. Do you or anyone else have any further info on looking after abutilon plants.
Many thanks, Elvira.

Hi
The bud drop problem is caused if the conditions you grow them in do not fit. That a general problem. Semishade and slightly moist outdoors is the best situation for them.
Dry heat, bad soil conditions and Abutilon virus enforce the problem.