diff --git a/rust/perspective-client/src/rust/config/view_config.rs b/rust/perspective-client/src/rust/config/view_config.rs
index fa4f36e..360b816 100644
--- a/rust/perspective-client/src/rust/config/view_config.rs
+++ b/rust/perspective-client/src/rust/config/view_config.rs
@@ -526,6 +526,23 @@ impl ViewConfig {
         }
     }
 
+    /// `_apply` for a field which is itself `Option`, where `None` in the update
+    /// means "not mentioned" rather than "clear it". `Option<Option<T>>` would be
+    /// needed to express both, and the wire format cannot carry the difference:
+    /// these fields are `skip_serializing_if = "Option::is_none"`, so an absent
+    /// field and an explicit null arrive identically. To lift a depth, send the
+    /// number of levels on that axis rather than clearing it.
+    fn _apply_optional<T: PartialEq>(field: &mut Option<T>, update: Option<T>) -> bool {
+        match update {
+            None => false,
+            Some(_) if *field == update => false,
+            Some(_) => {
+                *field = update;
+                true
+            },
+        }
+    }
+
     pub fn reset(&mut self, reset_expressions: bool) {
         let mut config = Self::default();
         if !reset_expressions {
@@ -568,6 +585,16 @@ impl ViewConfig {
         changed = Self::_apply(&mut self.windows, update.windows) || changed;
         changed = Self::_apply(&mut self.group_rollup_mode, update.group_rollup_mode) || changed;
         changed = Self::_apply(&mut self.split_rollup_mode, update.split_rollup_mode) || changed;
+
+        // Without these two, a depth can be set when a view is created --
+        // `table.view({ group_by_depth })` -- but never through `restore()`, which
+        // merges a `ViewConfigUpdate` onto the live config. The field arrives,
+        // deserializes, and is then dropped here, so the viewer's config and the
+        // engine never see it and nothing happens. That makes expand/collapse
+        // unreachable for anything driven by `restore()`, which is how a viewer
+        // changes its own configuration.
+        changed = Self::_apply_optional(&mut self.group_by_depth, update.group_by_depth) || changed;
+        changed = Self::_apply_optional(&mut self.split_by_depth, update.split_by_depth) || changed;
         if self.group_rollup_mode == GroupRollupMode::Total && !self.group_by.is_empty() {
             tracing::info!("`total` incompatible with `group_by`");
             changed = true;