My only qualification for posting here is that I tried (but failed) to get Regle's ukulele adjusted to make it easier to play, and I make ukuleles as well as flying gliders.
The hot glue pots which Danny remembers were hide glue - fine for furniture and musical instruments but not suitable for aircraft, as they release with damp and heat. Leaving a uke or guitar in a car on a hot day may well cause glue failure. Not much used by De Havilland I'd guess.
Casein glue is based on milk proteins, so I'm not surprised it didn't work well in India. There are still some 1930s gliders flying, held together with casein glue, but the joints get inspected very regularly!
For those interested in woodworking the Mosquito construction is quite a miracle, and shows how good wood is for making aircraft (so long as the glue holds
).