Given how they are little more than a modifier applied to the petrol injector timings, they could be merged on drifted block learn values...hence the reset the learns and run on petrol then re-merge the LPG
Yes, if it's actually being used on LPG, then it only collects data on petrol running when cold and mostly open-loop, so, before making any judgements, it's worth clearing the fuel trims, clearing the collected data in the LPG ECU and collecting fresh data on both petrol and (after that) LPG.
Okay, so in gonad language
Un plug the MAF.
Drive around the block on petrol.
Reset any codes which should clear the short / long term trims.
Drive on petrol only for a couple of days to let the car ecu sort out its new trims.
If long term are both zero switch to lpg, wipe gas and petrol maps.
Re record petrol map for the stag ecu then re calibrate the gas side
If the LT trims have both wandered, its liable to be a air leak or MAF problem.
If one sides trims are wandering, I should be looking at the lambda's on that side
Apologies for more questions but i'm the sort of bloke who needs to understand what / why i'm doing something
Not just follow blindly