Don't clear fg char if it's null or ' '

src/Terminal.ts

@@ -2046,7 +2046,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
   public blankLine(cur?: boolean, isWrapped?: boolean, cols?: number): LineData {
     const attr = cur ? this.eraseAttr() : this.defAttr;
 
-    const ch: CharData = [attr, ' ', 1]; // width defaults to 1 halfwidth character
+    const ch: CharData = [attr, ' ', 1, 32 /* ' '.charCodeAt(0) */]; // width defaults to 1 halfwidth character
     const line: LineData = [];
 
     // TODO: It is not ideal that this is a property on an array, a buffer line

src/renderer/ForegroundRenderLayer.ts

@@ -50,10 +50,12 @@ export class ForegroundRenderLayer extends BaseRenderLayer implements IDataRende
           this._state.cache[x][y] = charData;
           continue;
         }
-        this._state.cache[x][y] = charData;
 
-        // Clear the old character
-        this.clearCells(x, y, 1, 1);
+        // Clear the old character if present
+        if (state && state[CHAR_DATA_CODE_INDEX] !== 32 /*' '*/) {
+          this.clearCells(x, y, 1, 1);
+        }
+        this._state.cache[x][y] = charData;
 
         // Skip rendering if the character is invisible
         if (!code || code === 32 /*' '*/) {