"When we've initially started [..], dominant was Go 1.3, which had mechanisms to detect memory blocks allocated inside used libraries and all such blocks were to be freed by GC. Go 1.6 significantly improved its memory management, however as part of those improvements memory allocated by external libraries was no longer garbage collected by the runtime."

This looks like a serious API break.

To be fair, the whole idea of the runtime automagically managing external memory gives me shivers, and this looks like moving in the right direction - I just think it was not very wise to go with that initial decision in the first place.