I recently encountered the same problem using FreeRTOS+IO V1.0.1 with FreeRTOS V7.5.2....
I recently encountered the same problem. Looking in the archives (http://www.freertos.org/FreeRTOS_Support_Forum_Archive/September_2012/freertos_FreeRTOS_Plus_IO_LPC1769_UART_IRQ_Handler_5681883.html),...
FreeRTOS+IO Char Queue Rx potential infinite loop in ISR
FreeRTOS+IO Char Queue Tx timeout with empty queue