To reproduce:
Collapse code section, put cursor on it's visible first line, and then commented (ctrl-/)

Expected:
Collapsed code section gets commented

Actual:
The collapse marker disappears and only the first line gets commented. No apparent way is left to uncollapse the section, one needs to uncomment to be able to uncollapse.

(on the machine observed fakevim was used, unsure if that is relevant or not)