diff --git a/lib/shared/messages/multimedia-message-spec.js b/lib/shared/messages/multimedia-message-spec.js
--- a/lib/shared/messages/multimedia-message-spec.js
+++ b/lib/shared/messages/multimedia-message-spec.js
@@ -192,14 +192,15 @@
     messageData: MediaMessageData | ImagesMessageData,
     id: ?string,
   ): RawMediaMessageInfo | RawImagesMessageInfo {
-    if (messageData.type === messageTypes.IMAGES && id) {
-      return ({ ...messageData, id }: RawImagesMessageInfo);
-    } else if (messageData.type === messageTypes.IMAGES) {
-      return ({ ...messageData }: RawImagesMessageInfo);
+    const { sidebarCreation, ...rest } = messageData;
+    if (rest.type === messageTypes.IMAGES && id) {
+      return ({ ...rest, id }: RawImagesMessageInfo);
+    } else if (rest.type === messageTypes.IMAGES) {
+      return ({ ...rest }: RawImagesMessageInfo);
     } else if (id) {
-      return ({ ...messageData, id }: RawMediaMessageInfo);
+      return ({ ...rest, id }: RawMediaMessageInfo);
     } else {
-      return ({ ...messageData }: RawMediaMessageInfo);
+      return ({ ...rest }: RawMediaMessageInfo);
     }
   },
 
diff --git a/lib/shared/messages/text-message-spec.js b/lib/shared/messages/text-message-spec.js
--- a/lib/shared/messages/text-message-spec.js
+++ b/lib/shared/messages/text-message-spec.js
@@ -163,10 +163,11 @@
     messageData: TextMessageData,
     id: ?string,
   ): RawTextMessageInfo {
+    const { sidebarCreation, ...rest } = messageData;
     if (id) {
-      return { ...messageData, id };
+      return { ...rest, id };
     } else {
-      return { ...messageData };
+      return { ...rest };
     }
   },
 
diff --git a/lib/types/messages/images.js b/lib/types/messages/images.js
--- a/lib/types/messages/images.js
+++ b/lib/types/messages/images.js
@@ -3,7 +3,7 @@
 import type { Image } from '../media-types.js';
 import type { RelativeUserInfo } from '../user-types.js';
 
-export type ImagesMessageData = {
+type ImagesSharedBase = {
   +type: 14,
   +localID?: string, // for optimistic creations. included by new clients
   +threadID: string,
@@ -12,8 +12,13 @@
   +media: $ReadOnlyArray<Image>,
 };
 
+export type ImagesMessageData = {
+  ...ImagesSharedBase,
+  +sidebarCreation?: boolean,
+};
+
 export type RawImagesMessageInfo = {
-  ...ImagesMessageData,
+  ...ImagesSharedBase,
   +id?: string, // null if local copy without ID yet
 };
 
diff --git a/lib/types/messages/media.js b/lib/types/messages/media.js
--- a/lib/types/messages/media.js
+++ b/lib/types/messages/media.js
@@ -3,7 +3,7 @@
 import type { Media } from '../media-types.js';
 import type { RelativeUserInfo } from '../user-types.js';
 
-export type MediaMessageData = {
+type MediaSharedBase = {
   +type: 15,
   +localID?: string, // for optimistic creations. included by new clients
   +threadID: string,
@@ -12,8 +12,13 @@
   +media: $ReadOnlyArray<Media>,
 };
 
+export type MediaMessageData = {
+  ...MediaSharedBase,
+  +sidebarCreation?: boolean,
+};
+
 export type RawMediaMessageInfo = {
-  ...MediaMessageData,
+  ...MediaSharedBase,
   +id?: string, // null if local copy without ID yet
 };
 
diff --git a/lib/types/messages/text.js b/lib/types/messages/text.js
--- a/lib/types/messages/text.js
+++ b/lib/types/messages/text.js
@@ -2,7 +2,7 @@
 
 import type { RelativeUserInfo } from '../user-types.js';
 
-export type TextMessageData = {
+type TextSharedBase = {
   +type: 0,
   +localID?: string, // for optimistic creations. included by new clients
   +threadID: string,
@@ -11,8 +11,13 @@
   +text: string,
 };
 
+export type TextMessageData = {
+  ...TextSharedBase,
+  +sidebarCreation?: boolean,
+};
+
 export type RawTextMessageInfo = {
-  ...TextMessageData,
+  ...TextSharedBase,
   +id?: string, // null if local copy without ID yet
 };