Releasing other key in middle of the combo breaks the combo trigger

[ssbb]

I experience this a lot with combo V when typing fast. For example, in the A B C layout, you have a combo on A and B which outputs D. When you want to type CD, pressing C and then A+B often causes CAB to be output if C is released between the A and B presses.

Failing test: ssbb@672a399

I think it's related to the #1899 but not related to split sides as reported.