I'm using an MCP73833 (link to the datasheet) as the charging chip in one of my projects. We use its STAT1 pin (which is an open drain that goes to GND when a battery is being charged and floats if the battery is fully charged, or no battery is connected) to interface with a microcontroller to play an LED effect when the charge is underway and another one when it's completed. The pin is pulled high with a 10k resistor, and the GPIO pin of the microcontroller is also pulled high internally. Our current design follows the recommended design on the datasheet with some changes to accommodate our needs (nothing critical, things like max current, etc.)
So far, everything worked as expected, but we wanted to also add an LED to the same pin to use as a second indication (for a very particular reason. I know it's redundant, it's a long story). When we added the LED, the LED turns on when a battery is being charged, as expected, but we noticed that the microcontroller would rarely detect a battery charging. After measuring the voltage at the pin, we noticed that the voltage was ~0.8V, and not 0V, well above the logic level for 0. If I cut the trace that goes to the microcontroller, then the LED works and the voltage at the pin goes to GND. I drew a small schematic, hope it helps.
So to sum up, we follow the recommended design of the charging chip and want to use STAT1 to know the status of the charge cycle. If we interface with a microcontroller, or we use an LED as an indication, the pin goes to GND, as expected. If we use both, then the pin shows ~0.8V, and only the LED turns on, but the voltage is too high for the μC to see a low level, and I just can't think why. I know that the current drawn by the LED is a tad above the typ sinking current of the STAT1 pin, but it's well within spec. I could also see that an internal pull down in the GPIO pin in the μC could cause a voltage rise if some of that current leaked into it, but that's not the case.