I2C stuck start

As the title says i have a problem with the I2C start condition getting stuck. It doesen’t happen always, and not always after the same amounts of i2c bus access.

To be more precise, the stuck looks like: i issue a start condition. and then, when SI bit should get rocketed up it doesn’t, as if there was a problem with the start condition.

I use the i2c in this application all the time (pretty heavily loaded). I’m using a lpc2138, the I2C bus runs at 400kHz. Even if i go back in the code with the debugger and command “clear start bit” it doesn’t get cleared, only option is reset. The pullups are 4k5.

I’m wondering if this is a “feature” of the lpc2138 series, or am i just “lucky”?