The previous fix should probably be in is connected rather than the write function so moving it there.

Author: geekylou

STM32F1/cores/maple/usb_serial.cpp

@@ -106,7 +106,7 @@ size_t n = 0;
 
 size_t USBSerial::write(const void *buf, uint32 len) {
 size_t n = 0;
-    if (!this->isConnected() || !usb_cdcacm_get_dtr() || !buf) {
+    if (!this->isConnected() || !buf) {
         return 0;
     }
 
@@ -199,7 +199,7 @@ uint8 USBSerial::pending(void) {
 }
 
 uint8 USBSerial::isConnected(void) {
-    return usb_is_connected(USBLIB) && usb_is_configured(USBLIB);
+    return usb_is_connected(USBLIB) && usb_is_configured(USBLIB) && usb_cdcacm_get_dtr();
 }
 
 uint8 USBSerial::getDTR(void) {