|I purchased a Monrovia|
I apologize for this delayed reply to your gardening question and hope it is still helpful to you.
I could find no reference to the plant being grafted in Monrovia's literature on that plant. I suggest you watch the plant this next year to note any distinct differences in the leaf form, size, etc. If you feel the branches that bloomed yellow are a different variety then pruning them out during the growing season is a viable option. However it may be that this year their blooms are more normal. You are in the southern end of that plant's adaptation range and as such the long hot humid summers can take their toll. Try to keep the soil adequately moist but take care to definitely not keep it soggy wet as this is very detrimental and can be deadly.
Thanks for the question. Best wishes for a wonderful gardening year in 2007. Please stop in again soon!