with regards to the PIA, its nothing personal against LBA.
LBA cant handle a B773 with a (very) heavy load, and right now PIA need to get its pax moving as quickly as possible. Its better for them to run B773's to the UK rather than A310's, hence why MAN has got your services for a while.
As for your monday flight, im pretty sure PIA didnt move it back to MAN just to p**s people off. If there was a growing trend of more LBA pax, or pax in general flying from MAN on a monday, thats where PIA thought best to utilise its resources.