ATmega8535 and USART post-initialisation delay required?

Is there a requirement to delay using the USART (at least for asynchronous transmission) for a period of time after initially setting it up and enabling interupts until transmitting the first character?

I ask, because when I set it up and then immediately use it to output a character (or string of characters), they are consistently wrong. I tried outputing the following string: "sys initialised". If I do this immediately after the setting up, I get (consistently) the output on the right (see below). However, if I wait for 128 microseconds (gcc _delay_loop_1(255)), I sometimes get the correct output and sometimes the wrong output (about 20% of the time, it's wrong). If I wait for approx. 43ms (gcc _delay_loop_2(65535)), then I seem to get the correct result each time I 'boot' my system.

The ATmega8535 datasheet does not seem to say that a delay is required.

The system runs in an infinite loop but uses interupts to write the characters from a software circular buffer into the USART. Each time the USART signals that its own buffer is empty, then the data from the circular buffer is transferred to the UDR a character at a time.

The necessity for this delay was not noticed before, since the previous owner of the project was writting some stuff to eeprom before outputting the first USART character and the problem didn't show - except occasionally I did notice some corrupted characters being output at startup.

The system does have 2 DC motors that spin for less than a second as power is applied until the I/O ports are set up, but the wrong column is always the same data - so, I don't think it is noise.

The system is running with a 6.000MHz crystal with the external clock pin enabled. I'm using: 1200baud, 8-bits, 1 stop, no parity.

(binary representation given because there are patterns that can be detected - the right side of the 'wrong' columns are generally the same as the left side of the 'correct' columns.)

correct wrong

Anyone got any suggestions or observations?

Thanks.