Terry, you can water gild on glass or bare gesso. Final surface and texture is different, but gold leaf should stick equally well. The bole we are using is there for three main reasons: providing the much needed under-color, to smooth gesso's surface and prevent water from being fast absorbed by gessoed surface. If you gilded on bare gesso, gold leaf still might be burnished but it would somewhat suffer from lack of contrasting under-color, gold leaf being transparent and becoming more so as you burnish and compress it. Reversely, the bole will keep the gilded surface moistened long enough for you to do the burnishing without scratching the gold. Like wet gilded surface totally dried gilded surface can't be burnished without a scratch. In this last situation you need to "oil" gold's surface by whipping it with your fingers first (but be aware that very greasy fingers would "tarnish" the gold).
Bole itself is not migrating up or down the hill during gilding. It can be washed though, if RSG% is low, and that situation will translate in your water size gradually becoming dirty with clay. RSG is solid in dried form and jelly if wet. It takes hot water to dissolve RGS and wash it away, for which reason water size is always used at room temperature. You don't need to concerne yourself with migration of any kind.
Initially I had suspected poor gilding techniques leading to poor adhesion but now I propose a different diagnosis. Gilded surfaces dry on high light spots first and much later down the slopes. It may be that in fact you attempt burnishing those areas too early. Burnishing is not a mechanical operation and you must check surface prior to attempting burnishing. You need to tap the gilded surface with the tip of your burnisher and listen for the sound. Tap 100% dried surfaces first, just to get used to the "dried" sound, and then tap the recently gilded areas. If the sound is "shy" soft there is still water in there and you must not attempt burnishing. When sound is 80% dried you may start burnishing with very light moves at first and coming back over as surface dries out. A good gilder must possess a fine ear to tell the right moment burnishing must start.
Hope this may help you.
Cornel