Thermal decomposition of group 2 permanganates
It is observed that true composition of alkaline earth metal manganate is not known. It is proposed to be a mixture of manganite-manganate and has a general formula, $\ce{R3Mn2O8.H2O}$. However the composition/formula varies according to given method of preparation. It is found on some instance that heating the permangantes of alkaline earth metal gives manganates while in other case it gives manganites.  


Mangesium permanagate is prone to decomposition and it explode
violently in aqueous solution giving oxygen, ozone and the
manganate?(the reaction product is not defined properly?)
Calcium manganate is formed by decomposing calcium
permanganate.
Strontium permanaganate is also prone to decomposition and
forms either manganite or manganate depending on reaction condition
but either way, strontium manganate is formed by heating
strontium manganite at 1600 °C.
Barium permanganate also decomposes at 320 °C to form barium
manganite but if the permanganate is mixed with barium hydroxide,
barium manganate of composition $\ce{Ba3Mn2O8.H2O}$ is formed.
The reaction of beryllium permanganate decomposition is unknown to
the best of my knowledge mainly due to poor study on the compound.