Yeah, it's an easy mistake to make without understanding that alpha textures convert solid brush geometry during the compilation process as there are no clear symptoms of the fact besides the leak.
For this reason it's good practice to set your default texture, ideally to "nodraw", but any non-alpha texture will do; and try to reduce any clipping/cloning of brushes you've painted already as these can transfer textures from one face to another brush (and usually on a face that is hidden between two parallel brushes making them difficult to find). I used to have a bad habit of dropping a brush into the world and slicing it up with the clip tool to produce multiple brushes as it was faster than manually creating each brush. But it can produce and multiply errors if something goes wrong with one so it's easier to create a new raw brush, clone it and use the manipulation tool on the cloned brushes and paint them at the end and never re-use the painted brushes. It's a bit more advanced using the vertex manipulator to shape your brushes over the clip tool, and the vertex manipulation can be a massive pain in the arse, especially when it only selects one vertice along an axis when it should all, but it's worth learning it as it produces more consistent results.
For this reason it's good practice to set your default texture, ideally to "nodraw", but any non-alpha texture will do; and try to reduce any clipping/cloning of brushes you've painted already as these can transfer textures from one face to another brush (and usually on a face that is hidden between two parallel brushes making them difficult to find). I used to have a bad habit of dropping a brush into the world and slicing it up with the clip tool to produce multiple brushes as it was faster than manually creating each brush. But it can produce and multiply errors if something goes wrong with one so it's easier to create a new raw brush, clone it and use the manipulation tool on the cloned brushes and paint them at the end and never re-use the painted brushes. It's a bit more advanced using the vertex manipulator to shape your brushes over the clip tool, and the vertex manipulation can be a massive pain in the arse, especially when it only selects one vertice along an axis when it should all, but it's worth learning it as it produces more consistent results.
