Problems with my 129 Perzina

[aido1968]

I bought a 129 upright Perzina about 12 months ago from Dawsons.
It has had including the free tune from the shop 7 full tunes so far.
I keep it in a very stable temperate room with no central heating on.
The piano is never moved.
I play a few hours each day as it is my profession but certainly no heavy duty pounding.
Within a few weeks of tuning notes will drop and the octaves become unstable.
Has any one else encountered this or can offer an explanation.
My tuner who is quite superb believes the floating sound board to be a possible cause.
Its such a shame as the tone of this piano is wonderfull,however I cannot record it as it wanders to quickly.
Help please?