COBRA violations are reported to the US DOL. However, what you describe is not a COBRA violation. It is, in fact, a fairly standard practice.
Your employer has no legal obligation whatsoever to keep your insurance in force until you decide to elect COBRA and submit your paperwork and check. If the employer/administrator take the maximum amount of time under the law to send you your COBRA paperwork and you likewise take the maximum amount of time allowed by law to submit the paperwork and check, it could conceiveably be nearly five months from the last day of your employment till the employer receives your first COBRA payment; six months in some cases. Nothing in the law requires your employer to keep your insurance in force, unpaid, for nearly six months. If so, you could get between five and six months of free insurance at your employers expense.
Rather, the law permits your employer to cancel your insurance and then reinstate it retroactively after he has received your first check.