Since you haven't gotten any other feedback I thought I'd give my 2p. The Lacacote is a stronger mix of shellac so you can expect that it'll be more difficult to rinse from a brush. But because it's shellac it doesn't matter if it dries stiff if you only use the brush for shellac, you can just soften it next time you go to use it by dunking in meths, then use as normal.
If you do want to get the brush completely clean though you'll have to use a much larger volume of meths as well as possibly needing a two-bath or three-bath rinsing setup. Using a commercial brush cleaner for the last step might work more effectively than pure meths, I've had good luck with this for brushes I use for a range of finishes and not just shellac.
About the white lumps, you should probably try contacting Mylands to check on this but I think it's wax that has settled out of solution and solidified, either the wax in the original shellac or the stearates they've added to it to improve sanding. This may be a sign the stuff is a little out of date because I used to get the same in a very old bottle of Flag sanding sealer.
