Copied into here from an email.

I have configured up a standard LCD display over i2c using a 23017 along with a rotary encoder on the same device. Although I can print to serial the status of the menu, and the menu when debug lines are added to serial is rendering properly, the display remains blank.

Configuration:
Genuine MEGA 2560
23017 expander
20x4 display on port B
Rotary encoder and switch on port A
Using standard LCD display renderer. Configuration has been confirmed by moving the lcd initialisation into another sketch and it works there.

This is a bug that I've now reproduced on a board with similar configuration. It will be fixed in 1.2 as it is absolutely critical.

This bug will be fixed and 1.2 code base will be merged back to master later today.

It was a complex interaction. The IoAbstractionRef relies on a pointer type, for which (logically when thought about) the pointer to the object must occur before it's passed to anything.

However, if you are creating lots of global variables, and relying on ordering and initialisation, it will not always work.

It's an important point and I'll document in the IoAbstraction docs to avoid anyone else hitting this.