I hope you have a fix coming?
I wouldn't call it a "fix", since it's not really a bug, it's just a difference in features between P3D4, which supported DX11, and P3D5 that doesn't, and the whole livery system was redesigned for DirectX, to get away from the clunky FSX method and the removal of some crucial features from DX12 we used and required ( DirectWrite to handle Fonts ).
As explained in other threads about this, P3D 5.1 added Render to Texture using HTML5, which might potentially be used to REWRITE all the parts which we used DirectX 11 for, but at this time is still incomplete, since it lacks features very important for us, like support for non-square textures to prevent waste of VRAM (considering all GSX liveries logos are non square ) and still has bugs that needs to be fixed ( HTML5 menus getting stuck ).
Assuming 5.2 would add support for non-square texture, and assuming it will work properly, and assuming it won't cause any fps or other performance problems, after it will come out, we can START working on a new method for custom liveries. This might take a while and, of course, it won't work with any older P3D 5 version.
It's possible we might offer some kind of alternative solution in the meantime, like making a set of liveries FSX-style, with thousands of Simobjects variations instead of the efficient Render to texture method. It will be only temporary, and it won't support text rendering ( no jetway numbers ), but at least it might give back multiple ( non-customizable ) liveries.