When you have a shader active and you spectate an entity, whether it has it's own shader or not, it will adjust your shader to match what the entity sees (usually default shader) which is fine, but when you stop spectating that entity it sets your shader back to default.
Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.