TXE bit not reset in USART communication
That SEEMS to be covered in the section labelled "Transmit and receive" about half way down.  Viz (especially see bold.)


Before data can be sent, the transmitter must first be enabled by setting the USARTx_CR1_TE bit in USARTx_CR1. According to the reference manual, immediately after setting this bit, an idle frame will be sent automatically. I could not observe this when repeatedly clearing and setting the TE bit. 

Before sending a character to the data register, you should test the USARTx_SR_TXE bit. 

This bit indicates that data register holds data not yet sent to the TDR shift register.  

There is no need to directly set or clear the TXE flag, it is cleared when data is written to USARTx_DR and set when that data is transferred to the TDR. An interrupt can be connected to this bit if you want to be sending data under interrupt control.

If you write to USARTx_DR when the shift register is empty, the data will go straight into the shift register, transmission will begin immediately and the TXE flag will will be immediately set.


Read more: http://www.micromouseonline.com/2009/12/31/stm32-usart-basics/#ixzz1pl0toOU6



Text starting at the bottom of page 606 and  Fig 225 on Page 607 [!!!!!!!!] in
 RM0033 Reference manual STM32F205xx, STM32F207xx, STM32F215xx and STM32F217xx
advanced ARM-based 32-bit MCU seems to relate.