make _twrite() wait for the first bytes to be output.

lib/program.js

@@ -1559,6 +1559,8 @@ Program.prototype._buffer = function(text) {
   this._buf = text;
 
   nextTick(this._flush);
+
+  return true;
 };
 
 Program.prototype.flush = function(text) {
@@ -1578,16 +1580,33 @@ Program.prototype._write = function(text) {
 // Example: `DCS tmux; ESC Pt ST`
 // Real: `DCS tmux; ESC Pt ESC \`
 Program.prototype._twrite = function(data) {
+  var self = this;
+
   if (this.tmux) {
     // Replace all STs with BELs so they can be nested within the DCS code.
     data = data.replace(/\x1b\\/g, '\x07');
+
     // Wrap in tmux forward DCS:
     data = '\x1bPtmux;\x1b' + data + '\x1b\\';
+
+    // If we've never even flushed yet, it means we're still in
+    // the normal buffer. Wait for alt screen buffer.
+    if (this.output.bytesWritten === 0) {
+      nextTick(function() {
+        self.flush();
+        self.output.write(data);
+      });
+      return true;
+    }
+
     // NOTE: Flushing the buffer is required in some cases.
+    // The DCS code must be at the start of the output.
     this.flush();
+
     // Write out raw now that the buffer is flushed.
     return this.output.write(data);
   }
+
   return this._write(data);
 };