Hi Sunnydays - as Dancinggirl says - if you are having bleeding then this means the lining has built up. The utrogestan does not cause the bleeding - but if you bled after using it vaginally this means that your lining was very ready to come away, and it (Utro) was doing its job very effectively.
If progestogens are taken at high doses and over a long duration per month ( or continuously) then they will prevent the lining building up - so when the dose is reduced there may only be a small bleed. The size of the bleed is dependent on the dose of oestrogen combined with the dose, duration and type of progestogen. You probably know that already - but just trying to say that if you bled on the utro - then you needed to!
Vaginal Utrogestan is very effective at clearing the lining - but as you say it can limit bedroom activites if taken monthly

- but much better if on a longer cycle!
I can't remember what oestrogen dose you are on and I think you are post-menopause. Also are you trying a longer cycle too? it is all a compromise. I would have increased my oestrogen dose slightly a long time ago - had I not preferred to be on a longer cycle to avoid frequent progesterone. So I keep my oestrogen dose at medium level to keep the bleeds manageable and pretty pain free ie nothing like my natural periods - which is what I can cope with in my 60's. There is no way I would want to go back to prop er heavy periods and period pains! If you are younger, as Dancgingirl says you might need to make some adjustment to oestrogen dosage to reduce the bleeding - or to take a longer course of a progestogen. Alternatively you could try a couple of months of say 21 days Provera per month (if you are OK with this prog) which should both shed your lining and then prevent it building up - and then go back to 12 days and see how you get on - hopefully bleeds would reduce?
It may well be the answer is to vary your regime slightly throughout the year to keep things manageable - and as you say if your womb lining is verified OK with regular scans, at least you don't have to worry on that score!
Hurdity x