I think you’re right: the mode I was thinking of is CH - F1, which unfortunately is the very first mode in the menu and is therefore the easiest to use. As you say, pressing the middle button once pauses the clock and pressing it twice resets it. However, a player might easily press the button twice by accident.
I became aware of this several years ago in an embarrassing incident where I was called to a board to make a ruling, and the first thing I did was to pause the clock. I must have accidentally pressed the button twice by mistake, because the clock reset to 5 minutes each. Unfortunately I hadn’t noted the times on the clock before pausing/resetting it, and I had to ask the players what times they remembered having on their clocks before it was reset. Since then I’ve always been careful to look at the times on a clock before pausing it.
I have to say that I don’t really like the rule that if a player calls the opponent’s flag with his own flag still up but his flag falls before he stops the clock it’s draw. In the regular rules, 16E says “The flag is considered to have fallen when either player points this out.” That being the case, shouldn’t that immediately end the game, provided that the time forfeit claim is valid? But rule 14G explicitly says that “If a player whose flag is still up claims a win on time but does not stop the clock in time to prevent the flag from falling, the game is drawn.” So even if I’m watching the game as a TD and I know for a fact that White’s flag was still up when he said “Flag!”, if his flag subsequently falls and Black points this out, I have to rule that the game is a draw.
The rule I would prefer is that a player who points out that his opponent’s flag has fallen while his own flag is still up wins, provided that this can be proven by clear and convincing evidence. A good way to preserve the evidence is to stop the clock, but this shouldn’t be essential.
Rule 6.11 in the FIDE Laws of Chess talks about the situation where “both flags have fallen and it is impossible to establish which flag fell first”. Thus, under FIDE rules (in regular games, or in rapidplay when there is adequate supervision of the games by the arbiters) if it can be proved that Black’s flag fell and White’s flag was still up White wins, regardless of what happened after that. However, in FIDE rapidplay when there is inadequate supervision, the FIDE rule is similar to the USCF rule: “2. To claim a win on time, the claimant must stop both clocks and notify the arbiter. For the claim to be successful, the claimant’s flag must remain up and his opponent’s flag down after the clocks have been stopped.” It seems to me that there should be an exception where there is clear evidence as to which flag fell first.
Of course as a USCF TD I have to enforce the rules as they’re written and not the way I’d like them to be. I think at future blitz tournaments in my announcements before the first round I’ll emphasize that the clock must be stopped after making a time forfeit claim, and suggest that Chronos clocks not be set in mode CH - F1.