On my Ubuntu 14.04 setup I am definitely seeing an interaction between using the spread function and whether windows maximize correctly or not.
However, it is slightly different from the OP.
It very often happens that a window shows the incorrect behaviour (i.e. maximizing does NOT merge its menubar with the main menubar). If I then activate spread, and then select THAT misbehaving window, it will maximize correctly. After this, other windows then show correct or incorrect behaviour, but I've not been able to find a pattern in that.
On my Ubuntu 14.04 setup I am definitely seeing an interaction between using the spread function and whether windows maximize correctly or not.
However, it is slightly different from the OP.
It very often happens that a window shows the incorrect behaviour (i.e. maximizing does NOT merge its menubar with the main menubar). If I then activate spread, and then select THAT misbehaving window, it will maximize correctly. After this, other windows then show correct or incorrect behaviour, but I've not been able to find a pattern in that.